Across the world, natural or regional languages differ in many ways, (e.g. in pluralization rules). Therefore, Internationalization became a complex problem and it is hard to provide tools for solving all problems at once. Sven Fuchs focused to provide an extensible framework and easy to use gem that is Ruby I18n (internationalization) gem. The Ruby I18n gem is mainly designed for translating your application to a single custom language other than English or for providing multi-language support for your ruby on rails application. The pivotal point of the new I18n api in Rails is the I18n module which is provided as a gem and shipped with Rails (starting from Rails 2.2) in ActiveSupport’s vendor directory. Therefore, during my presentation I will try to go over some of the advanced optional features and architecture of I18n gem. Besides, I will also try to cover begin with I18n gem, setup, benefits, the work flow, what's in? and what's not? Etc.

9. before_filter :set_locale
def set_locale
# if params[:locale] is nil then I18n.default_locale
will be used
I18n.locale = params[:locale]
end

11. # 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

12. # config/routes.rb
map.resources :books, :path_prefix => '/:locale'
# => www.example.com/nl/books
map.root '/:locale', :controller => “dashboard”

15. before_filter :set_locale
def set_locale
I18n.locale = extract_locale_from_uri
end

16. def extract_locale_from_tld
parsed_locale = request.host.split('.').last
I18n.available_locales.include?
(parsed_locale.to_sym) ? parsed_locale : nil
end

18. def set_locale
logger.debug = “* Accept-Language:
#{request.env['HTTP_ACCEPT_LANGUAGE']}”
I18n.locale =
extract_locale_from_accept_language_header
end

19. def extract_locale_from_accept_language_header
request.env['HTTP_ACCEPT_LANGUAGE'].scan(/^[a-z]
{2}/).first
end

20. en:
activerecord:
models:
user: foo
admin: bar
attributes:
user:
login: “Handle” # => will translate User
attribute “login” as “Handle”

21. en:
activerecord:
errors:
messages:
blank: “can not has nottin”
# => u = User.new
# => #<User id:nil, etc>
# => u.valid?
# => false
# => u.errors.on(:name)
# => “can not has nottin”

23. en:
activerecord:
errors:
messages:
already_registered: “u already is
{{model}}”
# => u.errors.on(:email)
# => “u already is foo”

24. en:
activerecord:
errors:
template:
header:
one: “1 error prohibted this {{model}} from being
saved”
other: “{{count}} errors prohibted this {{model}} from
being saved”
body: “There were problems with the following fields:”

25. i18n
i18n i18n
backend
backend core_ext helpers locales
exceptions
gettext
gettext
helpers
tag fallbacks locale
version

26. backend
Interpolation fast simple active_record
active_record
compiler
Interpolation gettext
base
compiler
missing
Interpolation helpers
cache
compiler
store_procs
Interpolation Interpolation
cascader compiler
compiler
Interpolation links translation
chain
compiler
Interpolation metadata
cldr
compiler
Interpolation pluralization
fallbacks
compiler

27. def default_locale(locale)
@@default_locale = locale.to_sym rescue nil
end

28. def backend
@@backend ||= Backend::Simple.new
end

29. module I18n
module Backend
class Simple
include Base
end
end
end

30. def available_locales
@@available_locales ||= backend.available_locales
end

33. def default_exception_handler(exception, locale, key,
options)
return exception.message if MissingTranslationData ===
exception
raise exception
end

35. def config
Thread.current[:i18n_config] ||= I18n::Config.new
end

37. I18n.t :invalid, :scope =>
[:active_record, :error_messages] # =>
I18n.translation :invalid :active_record.error_messa
ges.invalid

38. I18n.t :foo, :bar => 'baz' #=> 'foo baz'
I18n.t :foo, :count => 1 #=> 'foo'
I18n.t :foo, :count => 0 #=> 'foos'
I18n.t :foo, :count => 2 #=> 'foos'
I18n.t :foo, :default => 'bar'

39. def translate(&args)
options = args.pop if args.last.is_a?(Hash)
key = args.shift
locale = options && options.delete(:locale) ||
config.locale
raises = options && options.delete(:raise)
config.backend.translate(locale, key, options ||
{})
rescue I18n::ArgumentError => exception
raise exception if raises
handle_exception(exception, locale, key,
options)
end
alias :t :translate

40. def localize(object, options = {})
locale = options.delete(:locale) || config.locale
format = options.delete(:format) || :default
config.backend.localize(locale, object, format,
options)
end
alias :l :localize

41. def load_translations(*filenames)
filenames.each { |filename| load_file(filename) }
end

42. def load_file(filename)
type = File.extname(filename).tr('.', '').downcase
raise UnknownFileType.new(type, filename)
unless respond_to?(:”load_#(type)”)
data = send(:”load_#(type)”, filename)
data.each { |locale, d| merge_translation(locale,
d) }
end

43. def store_translations(locale, data, options = {})
merge_translations(locale, data, options)
end

44. def merge_translations(locale, data, options = {})
locale = locale.to_sym
translations[locale] ||= {}
separator = options[:separator] ||
I18n.default_separator
data = unwind_keys(data, separator)
data = deep_symbolized_keys(data)
merger = proc do |key, v1, v2|
Hash === v1 && Hash === v2 ?
v1.merge(v2, &merger) : (v2 || v1)
end
translations[locale].merge!(data, &merger)
end

45. def translate(locale, key, options = {})
raise InvalidLocale.new(locale) unless locale
return key.map { |k| translate(locale, k, options) } if
key.is_a?(Array)
if options.empty?
entry = resolve(locale, key, lookup(locale, key),
options)
raise(I18n::MissingTranslationData.new(locale, key,
options)) if entry.nil?

46. else
count, scope, default =
options.values_at(:count, :scope, :default)
values = options.reject { |name, value|
RESERVED_KEYS.include?(name) }
entry = lookup(locale, key, scope, options)
entry = entry.nil? && default ?
default(locale, key, default, options) :
resolve(locale, key, entry, options)

47. raise(I18n::MissingTranslationData.new(locale,
key, options)) if entry.nil?
entry = pluralize(locale, entry, count) if
count
entry = interpolate(locale, entry, values) if
values
end
entry
end

49. case match
when '%a' then I18n.t(:"date.abbr_day_names”, :locale =>
locale, :format => format)[object.wday]
when '%A' then I18n.t(:"date.day_names”, :locale =>
locale, :format => format)[object.wday]
when '%b' then I18n.t(:"date.abbr_month_names", :locale =>
locale, :format => format)[object.mon]

50. when '%B' then I18n.t(:"date.month_names", :locale =>
locale, :format => format)[object.mon]
when '%p' then I18n.t(:"time.#{object.hour <
12 ? :am : :pm}", :locale => locale, :format => format) if
object.respond_to? :hour
end

52. MissingTranslationData # no translation was found for the
requested key
InvalidLocale # the locale set to I18n.locale is invalid (e.g. nil)

54. I18n.backend = Globalize::Backend::Static.new

55. module I18n
def just_raise_that_exception(*args)
raise args.first
end
end
I18n.exception_handler = :just_raise_that_exception