How to use the I18n fallback features in Rails 3 - ruby-on-rails

Question

I am getting an "translation missing" error message from Rails 3:
activerecord:
notices:
messages:
success:
create: "Something was created"
models:
user:
success:
create: "Thanks for registration"
I18n.t("activerecord.notices.models.user.success.create")
# => "Thanks for registration"
I18n.t("activerecord.notices.models.book.success.create")
# => "translation missing: de, activerecord, notices, models, book, success, create"
I don't know why the book model doesn't get the fallback massage. I have set config.i18n.fallbacks = true.

Answer 1

I set in config/application.rb usually
config.i18n.fallbacks = [:de, :fr, :en]
So you can declare the order of the fallback.
But keep attention in some environments/*.rb the configuration is overwritten.

Answer 2

When a :default option is given, its value will be returned if the translation is missing:
I18n.t :missing, :default => 'Not here'
# => 'Not here'
More info here

Answer 3

In rails 3+, this is set in the config/environments files :
# Enable locale fallbacks for I18n (makes lookups for any locale fall back to
# the I18n.default_locale when a translation can not be found)
config.i18n.fallbacks = true

Answer 4

[Answer is for Rails 2]
Have you enabled fallbacks for your backend? Assuming it's Simple(based on yml in example):
Put this in an initializer:
require "i18n/backend/fallbacks"
I18n::Backend::Simple.send(:include, I18n::Backend::Fallbacks)
https://github.com/svenfuchs/i18n/wiki/Fallbacks

Answer 5

I believe the best way to handle a missing string, is to display a default locale, rather than an error message.
Add this line in application.rb to fallback to the english locale.
config.i18n.fallbacks = [:en]
In case you want to specify locale-specific fallbacks, you can use the following:
config.i18n.fallbacks = {:de => [:de,:en], :en => [:en,:de]}
Also, note that you can enable and disable fallbacks based on your environment.
So while on development it might make sense to have an error displayed, you can instead enable fallbacks in your environments/production.rb with the following:
config.i18n.fallbacks = true

Answer 6

There is a misunderstanding with the I18n Fallback feature.
This feature causes that when there is a missing translation exception (in this case, it happens when I18n fails to find the value associated with the "activerecord.notices.models.book.success.create" key in the locale files of your current language) I18n will lookup in the predefined list of fallbacks languages the value of the key that generated the missing translation exception, if it's found I18n will returned that value, but if it's not found in any of those other locale files I18n will return the missing translation exception.
So when you defined config.i18n.fallbacks = true, that doesn't mean that when a missing translation exception occurs, in this case:
I18n.t("activerecord.models.book.success.create")
# => "translation missing: de, activerecord, notices, models, book, success, create"
I18n will lookup a similar key in your locale files to return his value, could be:
I18n.t("activerecord.models.user.success.create")
# => "Thanks for registration"
What will happens it's that I18n will lookup in yours defaults fallback languages for the specific language where the missing translation exception has occurred.
A good example of usage will be:
# using :"en-US" as a default locale:
I18n.default_locale = :"en-US"
I18n.fallbacks[:es] # => [:es, :"en-US", :en]
Locales files:
es:
activerecord:
notices:
messages:
success:
create: "Algo fue creado"
models:
user:
success:
create: "Gracias por registrarte"
en-US:
activerecord:
...
models:
books:
success:
create: "The model was created"
Call in English site:
I18n.t("activerecord.models.books.success.create")
# => "The model was created"
Call in Spanish site:
#with config.i18n.fallbacks = false
I18n.t("activerecord.models.books.success.create")
# => "translation missing: es, activerecord, models, book, success, create"
#with config.i18n.fallbacks = true
I18n.t("activerecord.models.books.success.create")
# => "The model was created"
For more information check: https://github.com/ruby-i18n/i18n