gettext is an internationalization (i18n) and localization (l10n) system commonly used for writing multilingual programs. Gettext is a standard for i18n in different communities, meaning there is a great set of tooling for developers and translators.

1. Add :gettext to your list of dependencies in mix.exs:

```elixir
def deps do
  [{:gettext, "~> 0.13"}]
end
```

2. Ensure :gettext is started before your application:

```elixir
def application do
  [applications: [:gettext, :logger]]
end
```

3. Optional: add the :gettext compiler so your backends are recompiled when .po files change:

```elixir
def project do
  [compilers: [:gettext]    Mix.compilers]
end
```

Documentation for Gettext is available on Hex.

To use gettext, you must define a gettext module:

defmodule MyApp.Gettext do
  use Gettext, otp_app: :my_app
end

And invoke the gettext API, based on the *gettext functions:

import MyApp.Gettext

# Simple translation
gettext "Here is one string to translate"

# Plural translation
number_of_apples = 4
ngettext "The apple is ripe",
         "The apples are ripe",
         number_of_apples
#=> "The apples are ripe"

# Domain-based translation
dgettext "errors", "Here is an error message to translate"

Translations in gettext are stored in Portable Object files (.po). Such files must be placed at priv/gettext/en/LC_MESSAGES/domain.po, where en is the locale and domain is the domain (the default domain is called default).

For example, the translation to pt_BR of the first two *gettext calls in the snippet above must be placed in the priv/gettext/pt_BR/LC_MESSAGES/default.po file with contents:

msgid "Here is one string to translate"
msgstr "Aqui está um texto para traduzir"

msgid "Here is the string to translate"
msgid_plural "Here are the strings to translate"
msgstr[0] "Aqui está o texto para traduzir"
msgstr[1] "Aqui estão os textos para traduzir"

.po are text based and can be edited directly by translators. Some may even use existing tools for managing them, such as Poedit or poeditor.com.

Finally, because translations are based on strings, your source code does not lose readability as you still see literal strings, like gettext "here is an example", instead of paths like translate "some.path.convention".

Read the documentation for the Gettext module for more information on locales, interpolation, pluralization and other features.

gettext is able to automatically extract translations from your source code, alleviating developers and translators from the repetitive and error-prone work of maintaining translation files.

When extracted from source, translations are placed into .pot files, which are template files. Those templates files can then be merged into translation files for each specific locale your application is being currently translated to.

In other words, the typical workflow looks like this:

1. Add gettext calls to your source code. No need to touch translation files at this point as gettext will return the given string if no translation is available:

   gettext "Welcome back!"

2. Once changes to the source are complete, run mix gettext.extract to automatically sync all existing entries to .pot (template files) in priv/gettext:

   mix gettext.extract

3. .pot files can then be merged into locale-specific .po files with mix gettext.merge:

   Merge .pot into all locales

   mix gettext.merge priv/gettext

   Merge .pot into one specific locale

   mix gettext.merge priv/gettext --locale en

It is also possible to execute both the extract and merge operations in one step with mix gettext.extract --merge.

Copyright 2015 Plataformatec

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.