Ruby GetText, but 3.5x faster + 560x less memory + simple + clean namespace + threadsave + extendable + multiple backends + Rails3 ready
Latest commit 8ea909b Jun 23, 2018


GetText but 3.5 x faster, 560 x less memory, simple, clean namespace (7 vs 34) and threadsafe!

It supports multiple backends (.mo, .po, .yml files, Database(ActiveRecord + any other), Chain, Loggers) and can easily be extended.

Example Rails application


Hash FastGettext GetText ActiveSupport I18n::Simple
Speed* 0.82s 1.36s 4.88s 21.77s
RAM* 4K 8K 4480K 10100K
Included backends db, yml, mo, po, logger, chain mo yml (db/key-value/po/chain in other I18n backends)
*50.000 translations with ruby enterprise 1.8.6 through `rake benchmark`


1. Install

gem install fast_gettext

2. Add a translation repository

From mo files (traditional/default)

FastGettext.add_text_domain('my_app', path: 'locale')

Or po files (less maintenance than mo)

FastGettext.add_text_domain('my_app', path: 'locale', type: :po)
# :ignore_fuzzy => true to not use fuzzy translations
# :report_warning => false to hide warnings about obsolete/fuzzy translations

Or yaml files (use I18n syntax/indentation)

# A single locale can be segmented in multiple yaml files but they all should be
# named with a `qq.yml` suffix, where `qq` is the locale name.
FastGettext.add_text_domain('my_app', path: 'config/locales', type: :yaml)

Or database (scaleable, good for many locales/translators)

# db access is cached <-> only first lookup hits the db
require "fast_gettext/translation_repository/db"
FastGettext::TranslationRepository::Db.require_models #load and include default models
FastGettext.add_text_domain('my_app', type: :db, model: TranslationKey)

3. Choose text domain and locale for translation

Do this once in every Thread. (e.g. Rails -> ApplicationController)

FastGettext.text_domain = 'my_app'
FastGettext.available_locales = ['de','en','fr','en_US','en_UK'] # only allow these locales to be set (optional)
FastGettext.locale = 'de'

4. Start translating

include FastGettext::Translation
_('Car') == 'Auto'
_('not-found') == 'not-found'
s_('Namespace|not-found') == 'not-found'
n_('Axis','Axis',3) == 'Achsen' #German plural of Axis
_('Hello %{name}!') % {name: "Pete"} == 'Hello Pete!'

Managing translations


Generate .po or .mo files using GetText parser (example tasks at gettext_i18n_rails)

Tell Gettext where your .mo or .po files lie, e.g. for locale/de/my_app.po and locale/de/LC_MESSAGES/

FastGettext.add_text_domain('my_app', path: 'locale')

Use the original GetText to create and manage po/mo-files. (Work on a po/mo parser & reader that is easier to use has started, contributions welcome @ get_pomo )


Example migration for ActiveRecord
The default plural seperator is |||| but you may overwrite it (or suggest a better one..).

This is usable with any model DataMapper/Sequel or any other(non-database) backend, the only thing you need to do is respond to the self.translation(key, locale) call. If you want to use your own models, have a look at the default models to see what you want/need to implement.

To manage translations via a Web GUI, use a Rails application and the translation_db_engine


Try the gettext_i18n_rails plugin, it simplifies the setup.
Try the translation_db_engine, to manage your translations in a db.

Setting available_locales,text_domain or locale will not work inside the evironment.rb, since it runs in a different thread then e.g. controllers, so set them inside your application_controller.

# config/environment.rb after initializers
Object.send(:include, FastGettext::Translation)
FastGettext.add_text_domain('accounting', path: 'locale')
FastGettext.add_text_domain('frontend', path: 'locale')

# app/controllers/application_controller.rb
class ApplicationController ...
  include FastGettext::Translation
  before_filter :set_locale
  def set_locale
    FastGettext.available_locales = ['de','en',...]
    FastGettext.text_domain = 'frontend'
    FastGettext.set_locale(params[:locale] || session[:locale] || request.env['HTTP_ACCEPT_LANGUAGE'])
    session[:locale] = I18n.locale = FastGettext.locale

Advanced features

Abnormal pluralisation

Plurals are selected by index, think of it as ['car', 'cars'][index]
A pluralisation rule decides which form to use e.g. in english its count == 1 ? 0 : 1.
If you have any languages that do not fit this rule, you have to add a custom pluralisation rule.

Via Ruby:

FastGettext.pluralisation_rule = lambda{|count| count > 5 ? 1 : (count > 2 ? 0 : 2)}

Via mo/pofile:

Plural-Forms: nplurals=2; plural=n==2?3:4;

Plural expressions for all languages.


If you only use one text domain, setting FastGettext.default_text_domain = 'app' is sufficient and no more text_domain= is needed


If the simple rule of "first availble_locale or 'en'" is not suficcient for you, set FastGettext.default_locale = 'de'.


Fallback when no available_locales are set


If there is content from different locales that you wish to display, you should use the with_locale option as below:

FastGettext.with_locale 'gsw_CH' do
  FastGettext._('Car was successfully created.')
# => "Z auto isch erfolgriich gspeicharat worda."


You can use any number of repositories to find a translation. Simply add them to a chain and when the first cannot translate a given key, the next is asked and so forth.

repos = ['new', path: '....'),'old', path: '....')
FastGettext.add_text_domain 'combined', type: :chain, :chain: repos


In some cases you can benefit from using merge repositories as an alternative to chains. They behave nearly the same. The difference is in the internal data structure. While chain repos iterate over the whole chain for each translation, merge repositories select and store the first translation at the time a subordinate repository is added. This puts the burden on the load phase and speeds up the translations.

repos = ['new', :path: '....'),'old', :path: '....')
domain = FastGettext.add_text_domain 'combined', type: :merge, chain: repos

Downside of this approach is that you have to reload the merge repo each time a language is changed.

FastGettext.locale = 'de'


When you want to know which keys could not be translated or were used, add a Logger to a Chain:

repos = ['app', path: '....')'logger', type: :logger, callback: lambda{|key_or_array_of_ids| ... }),
FastGettext.add_text_domain 'combined', type: :chain, chain: repos

If the Logger is in position #1 it will see all translations, if it is in position #2 it will only see the unfound. Unfound may not always mean missing, if you choose not to translate a word because the key is a good translation, it will appear nevertheless. A lambda or anything that responds to call will do as callback. A good starting point may be examples/missing_translations_logger.rb.


Want a xml version ? Write your own TranslationRepository!

# fast_gettext/translation_repository/xxx.rb
module FastGettext
  module TranslationRepository
    class Wtf
      define initialize(name,options), [key], plural(*keys) and
      either inherit from TranslationRepository::Base or define available_locales and pluralisation_rule

Multi domain support

If you have more than one gettext domain, there are two sets of functions available:

include FastGettext::TranslationMultidomain

d_("domainname", "string") # finds 'string' in domain domainname
dn_("domainname", "string", "strings", 1) # ditto
# etc.

These are helper methods so you don't need to write:

FastGettext.text_domain = "domainname"

It is useful in Rails plugins in the views for example. The second set of functions are D functions which search for string in all domains. If there are multiple translations in different domains, it returns them in random order (depends on the Ruby hash implementation):

include FastGettext::TranslationMultidomain

D_("string") # finds 'string' in any domain
# etc.

Alternatively you can use merge repository to achieve the same behaviour.



  • Add a fallback for Iconv.conv in ruby 1.9.4 -> lib/fast_gettext/vendor/iconv
  • YML backend that reads ActiveSupport::I18n files


Mo/Po-file parsing from Masao Mutoh, see vendor/README


Michael Grosser
License: MIT, some vendor parts under the same license terms as Ruby (see headers)
Build Status