How to translate a Rails application.
Locales
# config/application.rb
config.i18n.available_locales = %i[de fr it]
config.i18n.default_locale = :de
config.i18n.fallbacks = trueAdd rails-i18n for ready-made date, number, and Active Record translations:
# Gemfile
gem "rails-i18n"Locale files
# config/locales/de.yml
de:
hello: "Hallo, %{name}!"
apples:
one: "1 Apfel"
other: "%{count} Äpfel"
pages:
thankyou:
title: "Danke"
body_html: "<strong>Vielen Dank</strong> für deine Anfrage."Use lazy lookup in views and controllers to avoid repeating the full key path:
# app/views/pages/thankyou.html.erb
<h1><%= t(".title") %></h1>
<%= t(".body_html") %>A key ending in _html (or a leaf named html) is marked safe and rendered without escaping.
URL routing
# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
around_action :switch_locale
def switch_locale(&)
locale = params[:locale] || I18n.default_locale
I18n.with_locale(locale, &)
end
def default_url_options
{ locale: I18n.locale }
end
end# config/routes.rb
scope "(:locale)", locale: /de|fr|it/ do
get "thankyou", to: "pages#thankyou"
get "terms", to: "pages#terms"
resource :submissions, only: %i[new create]
get "submissions", to: "submissions#new"
get "/", to: "submissions#new"
endSet lang on the layout so screen readers and search engines pick up the active locale:
# app/views/layouts/application.html.erb
<html lang="<%= I18n.locale %>">A minimal locale switcher:
<% I18n.available_locales.each do |l| %>
<%= link_to l.to_s.upcase, url_for(locale: l),
class: ("active" if I18n.locale == l) %>
<% end %>Dates and numbers
<%= l(Time.current, format: :short) %>
<%= number_to_currency(19.99) %>rails-i18n ships the formats. Override them per locale under date.formats, time.formats, and number.*.
Models and validations
# config/locales/de.yml
de:
activerecord:
models:
question:
one: "Frage"
other: "Fragen"
attributes:
question:
question: "Frage"
answer: "Antwort"
errors:
models:
question:
attributes:
answer:
blank: "muss ausgefüllt werden"Question.model_name.human and Question.human_attribute_name(:answer) resolve these automatically, so form labels and validation messages stay translated without extra wiring.
Field translation
Translatable columns for Ruby on Rails, stored in the model table itself
# Gemfile
gem "traco"# app/models/question.rb
class Question < ApplicationRecord
translates :question, :answer
endTraco expects per-locale columns like question_de, question_fr, question_it. For a heavier setup with a separate translations table, look at Mobility.
Finding missing keys
i18n-tasks scans the codebase for untranslated keys and unused entries:
bundle exec i18n-tasks missing
bundle exec i18n-tasks unused