For a long time I had never fully embraced how simple internationalisation (i18n) in Rails is, but once I started using it by default I felt like a silly pickle for not embracing it before.

Before I dive in

Useful tools

There are two main tools I use while developing to see the i18n in action. Firstly i18n-debug a rails gem that appends the i18n lookups to the logs. The second is Quick Language Switcher a chrome extension that allows you to change the Accept-Language header.

Internationalisation != Localisation

Internationalisation and Localisation are not the same thing, and when I was a newbie I used to get this confused far to often. The best way to remember the difference is:

• Internationalisation - Displaying your app in the language the user is requesting.
• Localisation - Displaying content in your app based upon the users physical location, for example using the users local currency.

How RoR decides on the locale to use

By default Rails will attempt to honour the Accept-Language header in the users HTTP request, and serve the translations saved in your /config/locales/*.yml files. If it can't find a translation in the users language it'll fallback to the default_locale, which is normally set to en.

Reloading locales during development

Rails by default only once parses the translations when you boot the app, this can make it a tad tricky when you're experimenting in development mode, to get around this add the following initialiser:

# config/initializers/reload_locale.rb
# from http://stackoverflow.com/a/20570652/445724
if Rails.env.development?
  locale_reloader = ActiveSupport::FileUpdateChecker.new(Dir["config/locales/*yml"]) do
     I18n.backend.reload!
  end

  ActionDispatch::Callbacks.to_prepare do
    locale_reloader.execute_if_updated
  end
end

This will automatically reload your locales when they change without you having to restart the app.

Where Rails magic does stuff for you

Input Placeholders

You can tell Rails to use the i18n placeholder by passing placeholder: true into the inputs options.

<%# app/views/messages/_form.html.erb %>
<%= form_for :message do "f| %>
  <%= f.input :name, placeholder: true %>
<% end %>

This'll search the i18n tree for the following key setup:

en:
  helpers:
    placeholder:
      message:
        name: "Your placeholder text here"

Labels

<%# app/views/messages/_form.html.erb %>
<%= form_for :message do "f| %>
  <%= f.label :name %>
<% end %>

en:
  helpers:
    label:
      message:
        name: "Name label"
  activerecord:
    attributes:
      message:
        name: "Name attribute (fallback for when label is nil)"

Submit buttons

You can change the value of your create and update submit buttons:

<%# app/views/messages/_form.html.erb %>
<%= form_for :message do "f| %>
  <%= f.submit %>
<% end %>

en:
  helpers:
    submit:
      message:
        create: "Create a new %{model}"
        update: "Save changes to %{model}"

However you can also specify the create/update terms one level up the tree to have this effect every model in your app by default:

en:
  helpers:
    submit:
      create: "Create a new %{model}"
      update: "Save changes to %{model}"

Model names

In the previous example I used the %{model} argument in the i18n. You can easily change the name of a model in the locale file like this:

en:
  activerecord:
    models:
      messages: "Queries"

Casually in controllers

One of my favourite places to use the i18n is in my controller for the notices and alerts:

# app/controllers/messages_controller.rb
MessagesController < BaseController
  def update
    # Some business logic

    return redirect_to:index, notice: t(".notice") if @resource.save
    render :edit, alert: t(".alert")
  end
end

en:
  messages:
    update:
      notice: "Message was successfully updated."
      alert: "Unable to update message."

Casually in views (With arguments)

You can also pass arguments into the i18n translate method, like so:

<% # app/views/messages/_sidebar.html.erb %>
<%= t ".pricing_information", price: number_to_currency(200, precision: 2) %>

en:
  messages:
    sidebar:
      pricing_information: "That'll cost %{price}"

This would return the text:

That'll cost $200.00

Alternatively if you start without a dot, it'll look from the start of the i18n tree, for example:

<% # app/views/messages/_sidebar.html.erb %>
<%= t "pricing_information", price: number_to_currency(200, precision: 2) %>

en:
  pricing_information: "That'll cost %{price}"