The Ruby I18n (shorthand for internationalization) gem which is shipped with Ruby on Rails (starting from Rails 2.2) provides an easy-to-use and extensible framework for translating your application to a single custom language other than English or for providing multi-language support in your application.
The process of “internationalization” usually means to abstract all strings and other locale specific bits (such as date or currency formats) out of your application. The process of “localization” means to provide translations and localized formats for these bits.*1
So, in the process of internationalizing your Rails application you have to:
Ensure you have support for i18n.
Tell Rails where to find locale dictionaries.
Tell Rails how to set, preserve and switch locales.
In the process of localizing your application you'll probably want to do the following three things:
Replace or supplement Rails' default locale — e.g. date and time formats, month names, Active Record model names, etc.
Abstract strings in your application into keyed dictionaries — e.g. flash messages, static text in your views, etc.
Store the resulting dictionaries somewhere.
This guide will walk you through the I18n API and contains a tutorial on how to internationalize a Rails application from the start.
After reading this guide, you will know:
NOTE: The Ruby I18n framework provides you with all necessary means for internationalization/localization of your Rails application. You may, however, use any of various plugins and extensions available, which add additional functionality or features. See the Rails I18n Wiki for more information.
Internationalization is a complex problem. Natural languages differ in so many ways (e.g. in pluralization rules) that it is hard to provide tools for solving all problems at once. For that reason the Rails I18n API focuses on:
providing support for English and similar languages out of the box
making it easy to customize and extend everything for other languages
As part of this solution, every static string in the Rails framework — e.g. Active Record validation messages, time and date formats — has been internationalized, so localization of a Rails application means “over-riding” these defaults.
Thus, the Ruby I18n gem is split into two parts:
The public API of the i18n framework — a Ruby module with public methods that define how the library works
A default backend (which is intentionally named Simple backend) that implements these methods
As a user you should always only access the public methods on the I18n module, but it is useful to know about the capabilities of the backend.
NOTE: It is possible (or even desirable) to swap the shipped Simple backend with a more powerful one, which would store translation data in a relational database, GetText dictionary, or similar. See section Using different backends below.
The most important methods of the I18n API are:
translate # Lookup text translations localize # Localize Date and Time objects to local formats
These have the aliases t and l so you can use them like this:
I18n.t 'store.title' I18n.l Time.now
There are also attribute readers and writers for the following attributes:
load_path # Announce your custom translation files locale # Get and set the current locale default_locale # Get and set the default locale exception_handler # Use a different exception_handler backend # Use a different backend
So, let's internationalize a simple Rails application from the ground up in the next chapters!
There are just a few simple steps to get up and running with I18n support for your application.
Following the convention over configuration philosophy, Rails will set up your application with reasonable defaults. If you need different settings, you can overwrite them easily.
Rails adds all .rb
and .yml
files from the
config/locales
directory to your translations load
path, automatically.
The default en.yml
locale in this directory contains a sample
pair of translation strings:
en: hello: "Hello world"
This means, that in the :en
locale, the key hello
will map to the Hello world string. Every string inside Rails is
internationalized in this way, see for instance Active Model validation
messages in the activemodel/lib/active_model/locale/en.yml
file or time and date formats in the activesupport/lib/active_support/locale/en.yml
file. You can use YAML or standard Ruby Hashes to store translations in the
default (Simple) backend.
The I18n library will use English as a default
locale, i.e. if you don't set a different locale,
:en
will be used for looking up translations.
NOTE: The i18n library takes a pragmatic approach to
locale keys (after some
discussion, including only the locale (“language”) part, like
:en
, :pl
, not the region part, like
:en-US
or :en-GB
, which are traditionally used
for separating “languages” and “regional setting” or “dialects”. Many
international applications use only the “language” element of a locale such
as :cs
, :th
or :es
(for Czech, Thai
and Spanish). However, there are also regional differences within different
language groups that may be important. For instance, in the
:en-US
locale you would have $ as a currency symbol, while in
:en-GB
, you would have £. Nothing stops you from separating
regional and other settings in this way: you just have to provide full
“English - United Kingdom” locale in a :en-GB
dictionary.
Various Rails I18n plugins such as
Globalize3 may help
you implement it.
The translations load path (I18n.load_path
)
is just a Ruby Array of paths to your translation files that will be loaded
automatically and available in your application. You can pick whatever
directory and translation file naming scheme makes sense for you.
NOTE: The backend will lazy-load these translations when a translation is looked up for the first time. This makes it possible to just swap the backend with something else even after translations have already been announced.
The default application.rb
files has instructions on how to
add locales from another directory and how to set a different default
locale. Just uncomment and edit the specific lines.
# The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded. # config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s] # config.i18n.default_locale = :de
For the sake of completeness, let's mention that if you do not want to
use the application.rb
file for some reason, you can always
wire up things manually, too.
To tell the I18n library where it can find your custom translation files you can specify the load path anywhere in your application - just make sure it gets run before any translations are actually looked up. You might also want to change the default locale. The simplest thing possible is to put the following into an initializer:
# in config/initializers/locale.rb # tell the I18n library where to find your translations I18n.load_path += Dir[Rails.root.join('lib', 'locale', '*.{rb,yml}')] # set default locale to something other than :en I18n.default_locale = :pt
If you want to translate your Rails application to a single
language other than English (the default locale), you can set
I18n.default_locale to your locale in application.rb
or an
initializer as shown above, and it will persist through the requests.
However, you would probably like to provide support for more locales in your application. In such case, you need to set and pass the locale between requests.
WARNING: You may be tempted to store the chosen locale in a session or a cookie, however do not do this. The locale should be transparent and a part of the URL. This way you won't break people's basic assumptions about the web itself: if you send a URL to a friend, they should see the same page and content as you. A fancy word for this would be that you're being RESTful. Read more about the RESTful approach in Stefan Tilkov’s articles. Sometimes there are exceptions to this rule and those are discussed below.
The setting part is easy. You can set the locale in a
before_action
in the ApplicationController
like
this:
before_action :set_locale def set_locale I18n.locale = params[:locale] || I18n.default_locale end
This requires you to pass the locale as a URL query parameter as in
http://example.com/books?locale=pt
. (This is, for example,
Google's approach.) So http://localhost:3000?locale=pt
will load the Portuguese localization, whereas
http://localhost:3000?locale=de
would load the German
localization, and so on. You may skip the next section and head over to the
Internationalize your application section, if you want to
try things out by manually placing the locale in the URL and reloading the
page.
Of course, you probably don't want to manually include the locale in
every URL all over your application, or want the URLs look differently,
e.g. the usual http://example.com/pt/books
versus
http://example.com/en/books
. Let's discuss the different
options you have.
One option you have is to set the locale from the domain name where your
application runs. For example, we want www.example.com
to load
the English (or default) locale, and www.example.es
to load
the Spanish locale. Thus the top-level domain name is used for
locale setting. This has several advantages:
The locale is an obvious part of the URL.
People intuitively grasp in which language the content will be displayed.
It is very trivial to implement in Rails.
Search engines seem to like that content in different languages lives at different, inter-linked domains.
You can implement it like this in your ApplicationController
:
before_action :set_locale def set_locale I18n.locale = extract_locale_from_tld || I18n.default_locale end # Get locale from top-level domain or return nil if such locale is not available # You have to put something like: # 127.0.0.1 application.com # 127.0.0.1 application.it # 127.0.0.1 application.pl # in your /etc/hosts file to try this out locally def extract_locale_from_tld parsed_locale = request.host.split('.').last I18n.available_locales.include?(parsed_locale.to_sym) ? parsed_locale : nil end
We can also set the locale from the subdomain in a very similar way:
# Get locale code from request subdomain (like http://it.application.local:3000) # You have to put something like: # 127.0.0.1 gr.application.local # in your /etc/hosts file to try this out locally def extract_locale_from_subdomain parsed_locale = request.subdomains.first I18n.available_locales.include?(parsed_locale.to_sym) ? parsed_locale : nil end
If your application includes a locale switching menu, you would then have something like this in it:
link_to("Deutsch", "#{APP_CONFIG[:deutsch_website_url]}#{request.env['REQUEST_URI']}")
assuming you would set APP_CONFIG[:deutsch_website_url]
to
some value like http://www.application.de
.
This solution has aforementioned advantages, however, you may not be able or may not want to provide different localizations (“language versions”) on different domains. The most obvious solution would be to include locale code in the URL params (or request path).
The most usual way of setting (and passing) the locale would be to include
it in URL params, as we did in the I18n.locale =
params[:locale]
before_action in the first example. We
would like to have URLs like www.example.com/books?locale=ja
or www.example.com/ja/books
in this case.
This approach has almost the same set of advantages as setting the locale from the domain name: namely that it's RESTful and in accord with the rest of the World Wide Web. It does require a little bit more work to implement, though.
Getting the locale from params
and setting it accordingly is
not hard; including it in every URL and thus passing it through the
requests is. To include an explicit option in every URL (e.g.
link_to( books_url(locale: I18n.locale))
) would be tedious and
probably impossible, of course.
Rails contains infrastructure for “centralizing dynamic decisions about the
URLs” in its [ApplicationController#default_url_options
](api.rubyonrails.org/classes/ActionController/Base.html#M000515,
which is useful precisely in this scenario: it enables us to set “defaults”
for url_for
and helper methods dependent on it (by implementing/overriding this
method).
We can include something like this in our
ApplicationController
then:
# app/controllers/application_controller.rb def default_url_options(options={}) logger.debug "default_url_options is passed options: #{options.inspect}\n" { locale: I18n.locale } end
Every helper method dependent on url_for
(e.g. helpers for
named routes like root_path
or root_url
, resource
routes like books_path
or books_url
, etc.) will
now automatically include the locale in the query string,
like this: http://localhost:3001/?locale=ja
.
You may be satisfied with this. It does impact the readability of URLs, though, when the locale “hangs” at the end of every URL in your application. Moreover, from the architectural standpoint, locale is usually hierarchically above the other parts of the application domain: and URLs should reflect this.
You probably want URLs to look like this:
www.example.com/en/books
(which loads the English locale) and
www.example.com/nl/books
(which loads the Dutch locale). This
is achievable with the “over-riding default_url_options
”
strategy from above: you just have to set up your routes with scoping
option in this way:
# config/routes.rb scope "/:locale" do resources :books end
Now, when you call the books_path
method you should get
"/en/books"
(for the default locale). An URL like
http://localhost:3001/nl/books
should load the Dutch locale,
then, and following calls to books_path
should return
"/nl/books"
(because the locale changed).
If you don't want to force the use of a locale in your routes you can use an optional path scope (denoted by the parentheses) like so:
# config/routes.rb scope "(:locale)", locale: /en|nl/ do resources :books end
With this approach you will not get a Routing Error
when
accessing your resources such as http://localhost:3001/books
without a locale. This is useful for when you want to use the default
locale when one is not specified.
Of course, you need to take special care of the root URL (usually
“homepage” or “dashboard”) of your application. An URL like
http://localhost:3001/nl
will not work automatically, because
the root to: "books#index"
declaration in your
routes.rb
doesn't take locale into account. (And rightly
so: there's only one “root” URL.)
You would probably need to map URLs like these:
# config/routes.rb get '/:locale' => 'dashboard#index'
Do take special care about the order of your routes, so
this route declaration does not “eat” other ones. (You may want to add it
directly before the root :to
declaration.)
NOTE: Have a look at two plugins which simplify work with routes in this way: Sven Fuchs's routing_filter and Raul Murciano's translate_routes.
In specific cases, it would make sense to set the locale from client-supplied information, i.e. not from the URL. This information may come for example from the users' preferred language (set in their browser), can be based on the users' geographical location inferred from their IP, or users can provide it simply by choosing the locale in your application interface and saving it to their profile. This approach is more suitable for web-based applications or services, not for websites — see the box about sessions, cookies and RESTful architecture above.
Accept-Language
¶ ↑One source of client supplied information would be an
Accept-Language
HTTP header. People may set
this in their browser or other clients (such as curl).
A trivial implementation of using an Accept-Language
header
would be:
def set_locale logger.debug "* Accept-Language: #{request.env['HTTP_ACCEPT_LANGUAGE']}" I18n.locale = extract_locale_from_accept_language_header logger.debug "* Locale set to '#{I18n.locale}'" end private def extract_locale_from_accept_language_header request.env['HTTP_ACCEPT_LANGUAGE'].scan(/^[a-z]{2}/).first end
Of course, in a production environment you would need much more robust code, and could use a plugin such as Iain Hecker's [http_accept_language](github.com/iain/http_accept_language/tree/master or even Rack middleware such as Ryan Tomayko's locale.
Another way of choosing the locale from client information would be to use a database for mapping the client IP to the region, such as GeoIP Lite Country. The mechanics of the code would be very similar to the code above — you would need to query the database for the user's IP, and look up your preferred locale for the country/region/city returned.
You can also provide users of your application with means to set (and possibly over-ride) the locale in your application interface, as well. Again, mechanics for this approach would be very similar to the code above — you'd probably let users choose a locale from a dropdown list and save it to their profile in the database. Then you'd set the locale to this value.
OK! Now you've initialized I18n support for your Ruby on Rails application and told it which locale to use and how to preserve it between requests. With that in place, you're now ready for the really interesting stuff.
Let's internationalize our application, i.e. abstract every locale-specific parts, and then localize it, i.e. provide necessary translations for these abstracts.
You most probably have something like this in one of your applications:
# config/routes.rb Yourapp::Application.routes.draw do root to: "home#index" end
# app/controllers/home_controller.rb class HomeController < ApplicationController def index flash[:notice] = "Hello Flash" end end
# app/views/home/index.html.erb <h1>Hello World</h1> <p><%= flash[:notice] %></p>
Obviously there are two strings that are localized to
English. In order to internationalize this code, replace
these strings with calls to Rails' #t
helper with
a key that makes sense for the translation:
# app/controllers/home_controller.rb class HomeController < ApplicationController def index flash[:notice] = t(:hello_flash) end end
# app/views/home/index.html.erb <h1><%=t :hello_world %></h1> <p><%= flash[:notice] %></p>
When you now render this view, it will show an error message which tells
you that the translations for the keys :hello_world
and
:hello_flash
are missing.
NOTE: Rails adds a t
(translate
) helper method to
your views so that you do not need to spell out I18n.t
all the
time. Additionally this helper will catch missing translations and wrap the
resulting error message into a <span
class="translation_missing">
.
So let's add the missing translations into the dictionary files (i.e. do the “localization” part):
# config/locales/en.yml en: hello_world: Hello world! hello_flash: Hello flash! # config/locales/pirate.yml pirate: hello_world: Ahoy World hello_flash: Ahoy Flash
There you go. Because you haven't changed the default_locale, I18n will use English. Your application now shows:
And when you change the URL to pass the pirate locale
(http://localhost:3000?locale=pirate
), you'll get:
NOTE: You need to restart the server when you add new locale files.
You may use YAML (.yml
) or plain Ruby (.rb
) files
for storing your translations in SimpleStore. YAML is the preferred option
among Rails developers. However, it has one big disadvantage. YAML is very
sensitive to whitespace and special characters, so the application may not
load your dictionary properly. Ruby files will crash your application on
first request, so you may easily find what's wrong. (If you encounter
any “weird issues” with YAML dictionaries, try putting the relevant portion
of your dictionary into a Ruby file.)
You can use variables in the translation messages and pass their values from the view.
# app/views/home/index.html.erb <%=t 'greet_username', user: "Bill", message: "Goodbye" %>
# config/locales/en.yml en: greet_username: "%{message}, %{user}!"
OK! Now let's add a timestamp to the view, so we can demo the
date/time localization feature as well. To localize the
time format you pass the Time object to I18n.l
or (preferably)
use Rails' #l
helper. You can pick a format by passing the
:format
option — by default the :default
format
is used.
# app/views/home/index.html.erb <h1><%=t :hello_world %></h1> <p><%= flash[:notice] %></p <p><%= l Time.now, format: :short %></p>
And in our pirate translations file let's add a time format (it's already there in Rails' defaults for English):
# config/locales/pirate.yml pirate: time: formats: short: "arrrround %H'ish"
So that would give you:
TIP: Right now you might need to add some more date/time formats in order
to make the I18n backend work as expected (at least for the
'pirate' locale). Of course, there's a great chance that
somebody already did all the work by translating Rails'
defaults for your locale. See the rails-i18n
repository at GitHub for an archive of various locale files. When you
put such file(s) in config/locales/
directory, they will
automatically be ready for use.
Rails 4.0 allows you to define inflection rules (such as rules for
singularization and pluralization) for locales other than English. In
config/initializers/inflections.rb
, you can define these rules
for multiple locales. The initializer contains a default example for
specifying additional rules for English; follow that format for other
locales as you see fit.
Rails 2.3 introduces another convenient localization feature: localized
views (templates). Let's say you have a BooksController in
your application. Your index action renders content in
app/views/books/index.html.erb
template. When you put a
localized variant of this template: index.es.html.erb
in the same directory, Rails will render content in this template, when the
locale is set to :es
. When the locale is set to the default
locale, the generic index.html.erb
view will be used. (Future
Rails versions may well bring this automagic localization to
assets in public
, etc.)
You can make use of this feature, e.g. when working with a large amount of static content, which would be clumsy to put inside YAML or Ruby dictionaries. Bear in mind, though, that any change you would like to do later to the template must be propagated to all of them.
When you are using the default SimpleStore shipped with the i18n library, dictionaries are stored in plain-text files on the disc. Putting translations for all parts of your application in one file per locale could be hard to manage. You can store these files in a hierarchy which makes sense to you.
For example, your config/locales
directory could look like
this:
|-defaults |---es.rb |---en.rb |-models |---book |-----es.rb |-----en.rb |-views |---defaults |-----es.rb |-----en.rb |---books |-----es.rb |-----en.rb |---users |-----es.rb |-----en.rb |---navigation |-----es.rb |-----en.rb
This way, you can separate model and model attribute names from text inside views, and all of this from the “defaults” (e.g. date and time formats). Other stores for the i18n library could provide different means of such separation.
NOTE: The default locale loading mechanism in Rails does not load locale files in nested dictionaries, like we have here. So, for this to work, we must explicitly tell Rails to look further:
# config/application.rb config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}')]
Do check the Rails i18n Wiki for list of tools available for managing translations.
You should have good understanding of using the i18n library now, knowing all necessary aspects of internationalizing a basic Rails application. In the following chapters, we'll cover it's features in more depth.
Covered are features like these:
looking up translations
interpolating data into translations
pluralizing translations
using safe HTML translations
localizing dates, numbers, currency, etc.
Translations are looked up by keys which can be both Symbols or Strings, so these calls are equivalent:
I18n.t :message I18n.t 'message'
The translate
method also takes a :scope
option
which can contain one or more additional keys that will be used to specify
a “namespace” or scope for a translation key:
I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]
This looks up the :record_invalid
message in the Active Record
error messages.
Additionally, both the key and scopes can be specified as dot-separated keys as in:
I18n.translate "activerecord.errors.messages.record_invalid"
Thus the following calls are equivalent:
I18n.t 'activerecord.errors.messages.record_invalid' I18n.t 'errors.messages.record_invalid', scope: :active_record I18n.t :record_invalid, scope: 'activerecord.errors.messages' I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]
When a :default
option is given, its value will be returned if
the translation is missing:
I18n.t :missing, default: 'Not here' # => 'Not here'
If the :default
value is a Symbol, it will be used as a key
and translated. One can provide multiple values as default. The first one
that results in a value will be returned.
E.g., the following first tries to translate the key :missing
and then the key :also_missing.
As both do not yield a result,
the string “Not here” will be returned:
I18n.t :missing, default: [:also_missing, 'Not here'] # => 'Not here'
To look up multiple translations at once, an array of keys can be passed:
I18n.t [:odd, :even], scope: 'errors.messages' # => ["must be odd", "must be even"]
Also, a key can translate to a (potentially nested) hash of grouped translations. E.g., one can receive all Active Record error messages as a Hash with:
I18n.t 'activerecord.errors.messages' # => {:inclusion=>"is not included in the list", :exclusion=> ... }
Rails implements a convenient way to look up the locale inside views. When you have the following dictionary:
es: books: index: title: "Título"
you can look up the books.index.title
value
inside app/views/books/index.html.erb
template like this (note the dot):
<%= t '.title' %>
In many cases you want to abstract your translations so that variables can be interpolated into the translation. For this reason the I18n API provides an interpolation feature.
All options besides :default
and :scope
that are
passed to #translate
will be interpolated to the translation:
I18n.backend.store_translations :en, thanks: 'Thanks %{name}!' I18n.translate :thanks, name: 'Jeremy' # => 'Thanks Jeremy!'
If a translation uses :default
or :scope
as an
interpolation variable, an I18n::ReservedInterpolationKey
exception is raised. If a translation expects an interpolation variable,
but this has not been passed to #translate
, an
I18n::MissingInterpolationArgument
exception is raised.
In English there are only one singular and one plural form for a given string, e.g. “1 message” and “2 messages”. Other languages (Arabic, Japanese, Russian and many more) have different grammars that have additional or fewer plural forms. Thus, the I18n API provides a flexible pluralization feature.
The :count
interpolation variable has a special role in that
it both is interpolated to the translation and used to pick a pluralization
from the translations according to the pluralization rules defined by CLDR:
I18n.backend.store_translations :en, inbox: { one: 'one message', other: '%{count} messages' } I18n.translate :inbox, count: 2 # => '2 messages' I18n.translate :inbox, count: 1 # => 'one message'
The algorithm for pluralizations in :en
is as simple as:
entry[count == 1 ? 0 : 1]
I.e. the translation denoted as :one
is regarded as singular,
the other is used as plural (including the count being zero).
If the lookup for the key does not return a Hash suitable for
pluralization, an 18n::InvalidPluralizationData
exception is
raised.
The locale can be either set pseudo-globally to I18n.locale
(which uses Thread.current
like, e.g., Time.zone
)
or can be passed as an option to #translate
and
#localize
.
If no locale is passed, I18n.locale
is used:
I18n.locale = :de I18n.t :foo I18n.l Time.now
Explicitly passing a locale:
I18n.t :foo, locale: :de I18n.l Time.now, locale: :de
The I18n.locale
defaults to I18n.default_locale
which defaults to :en
. The default locale can be set like
this:
I18n.default_locale = :de
Keys with a '_html' suffix and keys named 'html' are marked as HTML safe. Use them in views without escaping.
# config/locales/en.yml en: welcome: <b>welcome!</b> hello_html: <b>hello!</b> title: html: <b>title!</b>
# app/views/home/index.html.erb <div><%= t('welcome') %></div> <div><%= raw t('welcome') %></div> <div><%= t('hello_html') %></div> <div><%= t('title.html') %></div>
The Simple backend shipped with Active Support allows you to store translations in both plain Ruby and YAML format.*2
For example a Ruby Hash providing translations can look like this:
{ pt: { foo: { bar: "baz" } } }
The equivalent YAML file would look like this:
pt: foo: bar: baz
As you see, in both cases the top level key is the locale.
:foo
is a namespace key and :bar
is the key for
the translation “baz”.
Here is a “real” example from the Active Support en.yml
translations YAML file:
en: date: formats: default: "%Y-%m-%d" short: "%b %d" long: "%B %d, %Y"
So, all of the following equivalent lookups will return the
:short
date format "%b %d"
:
I18n.t 'date.formats.short' I18n.t 'formats.short', scope: :date I18n.t :short, scope: 'date.formats' I18n.t :short, scope: [:date, :formats]
Generally we recommend using YAML as a format for storing translations. There are cases, though, where you want to store Ruby lambdas as part of your locale data, e.g. for special date formats.
You can use the methods Model.model_name.human
and
Model.human_attribute_name(attribute)
to transparently look up
translations for your model and attribute names.
For example when you add the following translations:
en: activerecord: models: user: Dude attributes: user: login: "Handle" # will translate User attribute "login" as "Handle"
Then User.model_name.human
will return “Dude” and
User.human_attribute_name("login")
will return
“Handle”.
Active Record validation error messages can also be translated easily. Active Record gives you a couple of namespaces where you can place your message translations in order to provide different messages and translation for certain models, attributes, and/or validations. It also transparently takes single table inheritance into account.
This gives you quite powerful means to flexibly adjust your messages to your application's needs.
Consider a User model with a validation for the name attribute like this:
class User < ActiveRecord::Base validates :name, presence: true end
The key for the error message in this case is :blank
. Active
Record will look up this key in the namespaces:
activerecord.errors.models.[model_name].attributes.[attribute_name] activerecord.errors.models.[model_name] activerecord.errors.messages errors.attributes.[attribute_name] errors.messages
Thus, in our example it will try the following keys in this order and return the first result:
activerecord.errors.models.user.attributes.name.blank activerecord.errors.models.user.blank activerecord.errors.messages.blank errors.attributes.name.blank errors.messages.blank
When your models are additionally using inheritance then the messages are looked up in the inheritance chain.
For example, you might have an Admin model inheriting from User:
class Admin < User validates :name, presence: true end
Then Active Record will look for messages in this order:
activerecord.errors.models.admin.attributes.name.blank activerecord.errors.models.admin.blank activerecord.errors.models.user.attributes.name.blank activerecord.errors.models.user.blank activerecord.errors.messages.blank errors.attributes.name.blank errors.messages.blank
This way you can provide special translations for various error messages at different points in your models inheritance chain and in the attributes, models, or default scopes.
The translated model name, translated attribute name, and value are always available for interpolation.
So, for example, instead of the default error message "can not
be blank"
you could use the attribute name like this :
"Please fill in your %{attribute}"
.
count
, where available, can be used for pluralization if
present:
| validation | with option | message | interpolation | | ———— | ————————- | ————————- | ————- | | confirmation | - | :confirmation | - | | acceptance | - | :accepted | - | | presence | - | :blank | - | | length | :within, :in | :too_short | count | | length | :within, :in | :too_long | count | | length | :is | :wrong_length | count | | length | :minimum | :too_short | count | | length | :maximum | :too_long | count | | uniqueness | - | :taken | - | | format | - | :invalid | - | | inclusion | - | :inclusion | - | | exclusion | - | :exclusion | - | | associated | - | :invalid | - | | numericality | - | :not_a_number | - | | numericality | :greater_than | :greater_than | count | | numericality | :greater_than_or_equal_to | :greater_than_or_equal_to | count | | numericality | :equal_to | :equal_to | count | | numericality | :less_than | :less_than | count | | numericality | :less_than_or_equal_to | :less_than_or_equal_to | count | | numericality | :only_integer | :not_an_integer | - | | numericality | :odd | :odd | - | | numericality | :even | :even | - |
error_messages_for
Helper¶ ↑If you are using the Active Record error_messages_for
helper,
you will want to add translations for it.
Rails ships with the following translations:
en: activerecord: errors: template: header: one: "1 error prohibited this %{model} from being saved" other: "%{count} errors prohibited this %{model} from being saved" body: "There were problems with the following fields:"
NOTE: In order to use this helper, you need to install DynamicForm gem by
adding this line to your Gemfile: gem 'dynamic_form'
.
If you don't pass a subject to the mail
method, Action
Mailer will try to find it in your translations. The performed lookup will
use the pattern
<mailer_scope>.<action_name>.subject
to construct
the key.
# user_mailer.rb class UserMailer < ActionMailer::Base def welcome(user) #... end end
en: user_mailer: welcome: subject: "Welcome to Rails Guides!"
Rails uses fixed strings and other localizations, such as format strings and other format information in a couple of helpers. Here's a brief overview.
distance_of_time_in_words
translates and pluralizes its result
and interpolates the number of seconds, minutes, hours, and so on. See datetime.distance_in_words
translations.
datetime_select
and select_month
use translated
month names for populating the resulting select tag. See date.month_names
for translations. datetime_select
also looks up the order
option from date.order
(unless you pass the option explicitly). All date selection helpers
translate the prompt using the translations in the datetime.prompts
scope if applicable.
The number_to_currency
, number_with_precision
,
number_to_percentage
, number_with_delimiter
, and
number_to_human_size
helpers use the number format settings
located in the number
scope.
model_name.human
and human_attribute_name
use
translations for model names and attribute names if available in the activerecord.models
scope. They also support translations for inherited class names (e.g. for
use with STI) as explained above in “Error message scopes”.
ActiveModel::Errors#generate_message
(which is used by Active
Model validations but may also be used manually) uses
model_name.human
and human_attribute_name
(see
above). It also translates the error message and supports translations for
inherited class names as explained above in “Error message scopes”.
ActiveModel::Errors#full_messages
prepends the attribute name
to the error message using a separator that will be looked up from errors.format
(and which defaults to "%{attribute} %{message}"
).
Array#to_sentence
uses format settings as given in the support.array
scope.
For several reasons the Simple backend shipped with Active Support only does the “simplest thing that could possibly work” for Ruby on Rails*3 … which means that it is only guaranteed to work for English and, as a side effect, languages that are very similar to English. Also, the simple backend is only capable of reading translations but can not dynamically store them to any format.
That does not mean you're stuck with these limitations, though. The Ruby I18n gem makes it very easy to exchange the Simple backend implementation with something else that fits better for your needs. E.g. you could exchange it with Globalize's Static backend:
I18n.backend = Globalize::Backend::Static.new
You can also use the Chain backend to chain multiple backends together. This is useful when you want to use standard translations with a Simple backend but store custom application translations in a database or other backends. For example, you could use the Active Record backend and fall back to the (default) Simple backend:
I18n.backend = I18n::Backend::Chain.new(I18n::Backend::ActiveRecord.new, I18n.backend)
The I18n API defines the following exceptions that will be raised by backends when the corresponding unexpected conditions occur:
MissingTranslationData # no translation was found for the requested key InvalidLocale # the locale set to I18n.locale is invalid (e.g. nil) InvalidPluralizationData # a count option was passed but the translation data is not suitable for pluralization MissingInterpolationArgument # the translation expects an interpolation argument that has not been passed ReservedInterpolationKey # the translation contains a reserved interpolation variable name (i.e. one of: scope, default) UnknownFileType # the backend does not know how to handle a file type that was added to I18n.load_path
The I18n API will catch all of these exceptions when they are thrown in the
backend and pass them to the default_exception_handler method. This method
will re-raise all exceptions except for MissingTranslationData
exceptions. When a MissingTranslationData
exception has been
caught, it will return the exception’s error message string containing the
missing key/scope.
The reason for this is that during development you'd usually want your views to still render even though a translation is missing.
In other contexts you might want to change this behavior, though. E.g. the
default exception handling does not allow to catch missing translations
during automated tests easily. For this purpose a different exception
handler can be specified. The specified exception handler must be a method
on the I18n module or a class with #call
method:
module I18n class JustRaiseExceptionHandler < ExceptionHandler def call(exception, locale, key, options) if exception.is_a?(MissingTranslation) raise exception.to_exception else super end end end end I18n.exception_handler = I18n::JustRaiseExceptionHandler.new
This would re-raise only the MissingTranslationData
exception,
passing all other input to the default exception handler.
However, if you are using I18n::Backend::Pluralization
this
handler will also raise I18n::MissingTranslationData: translation
missing: en.i18n.plural.rule
exception that should normally be
ignored to fall back to the default pluralization rule for English locale.
To avoid this you may use additional check for translation key:
if exception.is_a?(MissingTranslation) && key.to_s != 'i18n.plural.rule' raise exception.to_exception else super end
Another example where the default behavior is less desirable is the Rails
TranslationHelper which provides the method #t
(as well as
#translate
). When a MissingTranslationData
exception occurs in this context, the helper wraps the message into a span
with the CSS class translation_missing
.
To do so, the helper forces I18n#translate
to raise exceptions
no matter what exception handler is defined by setting the
:raise
option:
I18n.t :foo, raise: true # always re-raises exceptions from the backend
At this point you should have a good overview about how I18n support in Ruby on Rails works and are ready to start translating your project.
If you find anything missing or wrong in this guide, please file a ticket on our issue tracker. If you want to discuss certain portions or have questions, please sign up to our mailing list.
I18n support in Ruby on Rails was introduced in the release 2.2 and is still evolving. The project follows the good Ruby on Rails development tradition of evolving solutions in plugins and real applications first, and only then cherry-picking the best-of-breed of most widely useful features for inclusion in the core.
Thus we encourage everybody to experiment with new ideas and features in plugins or other libraries and make them available to the community. (Don't forget to announce your work on our mailing list)
If you find your own locale (language) missing from our example translations data repository for Ruby on Rails, please fork the repository, add your data and send a pull request.
rails-i18n.org - Homepage of the rails-i18n project. You can find lots of useful resources on the wiki.
Google group: rails-i18n - The project's mailing list.
GitHub: rails-i18n - Code repository for the rails-i18n project. Most importantly you can find lots of example translations for Rails that should work for your application in most cases.
GitHub: i18n - Code repository for the i18n gem.
Lighthouse: rails-i18n - Issue tracker for the rails-i18n project.
Lighthouse: i18n - Issue tracker for the i18n gem.
Sven Fuchs (initial author)
If you found this guide useful, please consider recommending its authors on workingwithrails.
^1 Or, to quote [Wikipedia](en.wikipedia.org/wiki/Internationalization_and_localization:) _“Internationalization is the process of designing a software application so that it can be adapted to various languages and regions without engineering changes. Localization is the process of adapting software for a specific region or language by adding locale-specific components and translating text.”_
^2 Other backends might allow or require to use other formats, e.g. a GetText backend might allow to read GetText files.
^3 One of these reasons is that we don't want to imply any unnecessary load for applications that do not need any I18n capabilities, so we need to keep the I18n library as simple as possible for English. Another reason is that it is virtually impossible to implement a one-fits-all solution for all problems related to I18n for all existing languages. So a solution that allows us to exchange the entire implementation easily is appropriate anyway. This also makes it much easier to experiment with custom features and extensions.