gettext v0.15.0 Gettext View Source
The Gettext
module provides a
gettext-based API for working with
internationalized applications.
Using Gettext
To use Gettext
, a module that calls use Gettext
has to be defined:
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app
end
This automatically defines some macros in the MyApp.Gettext
module.
Here are some examples:
import MyApp.Gettext
# Simple translation
gettext "Here is the string to translate"
# Plural translation
ngettext "Here is the string to translate",
"Here are the strings to translate",
3
# Domain-based translation
dgettext "errors", "Here is the error message to translate"
Translations are looked up from .po
files. In the following sections we will
explore exactly what are those files before we explore the “Gettext API” in
detail.
Translations
Translations are stored inside PO (Portable Object) files, with a .po
extension. For example, this is a snippet from a PO file:
# This is a comment
msgid "Hello world!"
msgstr "Ciao mondo!"
PO files containing translations for an application must be stored in a
directory (by default it’s priv/gettext
) that has the following struture:
gettext directory
└─ locale
└─ LC_MESSAGES
├─ domain_1.po
├─ domain_2.po
└─ domain_3.po
Here, locale
is the locale of the translations (for example, en_US
),
LC_MESSAGES
is a fixed directory, and domain_i.po
are PO files containing
domain-scoped translations. For more information on domains, check out the
“Domains” section below.
A concrete example of such a directory structure could look like this:
priv/gettext
└─ en_US
| └─ LC_MESSAGES
| ├─ default.po
| └─ errors.po
└─ it
└─ LC_MESSAGES
├─ default.po
└─ errors.po
By default, Gettext expects translations to be stored under the priv/gettext
directory of an application. This behaviour can be changed by specifying a
:priv
option when using Gettext
:
# Look for translations in my_app/priv/translations instead of
# my_app/priv/gettext
use Gettext, otp_app: :my_app, priv: "priv/translations"
The translations directory specified by the :priv
option should be a directory
inside priv/
, otherwise some things (like mix compile.gettext
) won’t work
as expected.
Locale
At runtime, all gettext-related functions and macros that do not explicitly take a locale as an argument read the locale from the backend locale and fallbacks to Gettext’s locale.
Gettext.put_locale/1
can be used to change the locale of all backends for
the current Elixir process. That’s the preferred mechanism for setting the
locale at runtime. Gettext.put_locale/2
can be used when you want to set the
locale of one specific Gettext backend without affecting other Gettext
backends.
Similarly, Gettext.get_locale/0
gets the locale for all backends in the
current process. Gettext.get_locale/1
gets the locale of a specific backend
for the current process. Check their documentation for more information.
Locales are expressed as strings (like "en"
or "fr"
); they can be
arbitrary strings as long as they match a directory name. As mentioned above,
the locale is stored per-process (in the process dictionary): this means
that the locale must be set in every new process in order to have the right
locale available for that process. Pay attention to this behaviour, since not
setting the locale will not result in any errors when Gettext.get_locale/0
or Gettext.get_locale/1
are called called; the default locale will be
returned instead.
To decide which locale to use, each gettext-related function in a given backend follows these steps:
- if there is a backend-specific locale for the given backend for this
process (see
put_locale/2
), use that, otherwise - if there is a global locale for this process (see
put_locale/1
), use that, otherwise - if there is a backend-specific default locale in the configuration for
that backend’s
:otp_app
(see the “Default locale” section below), use that, otherwise - use the default global Gettext locale (see the “Default locale” section below)
Default locale
The value of the default locale for a
given Gettext backend can be set in the configuration for the :otp_app
of
that Gettext backend. For example, in the config/config.exs
file of the
my_app
application:
config :my_app, MyApp.Gettext,
default_locale: "fr"
This option is read dynamically every time the locale has not been explicitly
set, so to change the default locale of a backend for all processes at runtime
it’s enough to use Application.put_env/4
. There’s no default
backend-specific locale.
The global Gettext default locale can be configured through the
:default_locale
key of the :gettext
application:
config :gettext, :default_locale, "fr"
By default the global locale is "en"
. See also get_locale/0
and
put_locale/1
.
Gettext API
There are two ways to use gettext:
- using macros from your own gettext module, like
MyApp.Gettext
- using functions from the
Gettext
module
These two approaches are different and each one has its own use case.
Using macros
Each module that calls use Gettext
is usually referred to as a “Gettext
backend”, as it implements the Gettext.Backend
behaviour. When a module
calls use Gettext
, the following macros are automatically
defined inside it:
gettext/2
dgettext/3
ngettext/4
dngettext/5
gettext_noop/1
,dgettext_noop/2
,ngettext_noop/3
,dngettext_noop/4
Supposing the caller module is MyApp.Gettext
, the macros mentioned above
behave as follows:
gettext(msgid, bindings \\ %{})
- likeGettext.gettext(MyApp.Gettext, msgid, bindings)
dgettext(domain, msgid, bindings \\ %{})
- likeGettext.dgettext(MyApp.Gettext, domain, msgid, bindings)
ngettext(msgid, msgid_plural, n, bindings \\ %{})
- likeGettext.ngettext(MyApp.Gettext, msgid, msgid_plural, n, bindings)
dngettext(domain, msgid, msgid_plural, n, bindings \\ %{})
- likeGettext.dngettext(MyApp.Gettext, domain, msgid, msgid_plural, n, bindings)
*_noop
family of functions - used to mark translations for extraction without translating them; see the documentation for these macros inGettext.Backend
See also the Gettext.Backend
behaviour for more detailed documentation about
these macros.
Using macros is preferred as gettext is able to automatically sync the
translations in your code with PO files. This, however, imposes a constraint:
arguments passed to any of these macros have to be strings at compile
time. This means that they have to be string literals or something that
expands to a string literal at compile time (for example, a module attribute like
@my_string "foo"
).
These are all valid uses of the gettext macros:
Gettext.put_locale MyApp.Gettext, "it"
MyApp.Gettext.gettext "Hello world"
#=> "Ciao mondo"
@msgid "Hello world"
MyApp.Gettext.gettext @msgid
#=> "Ciao mondo"
The gettext
/dgettext
/ngettext
/dngettext
macros raise an
ArgumentError
exception if they receive a domain
, msgid
, or
msgid_plural
that doesn’t expand to a string at compile time:
msgid = "Hello world"
MyApp.Gettext.gettext msgid
#=> ** (ArgumentError) msgid must be a string literal
Using compile-time strings isn’t always possible. For this reason,
the Gettext
module provides a set of functions as well.
Using functions
If compile-time strings cannot be used, the solution is to use the functions
in the Gettext
module instead of the macros described above. These functions
perfectly mirror the macro API, but they all expect a module name as the first
argument. This module has to be a module which calls use Gettext
. For example:
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app
end
Gettext.put_locale MyApp.Gettext, "pt_BR"
msgid = "Hello world"
Gettext.gettext(MyApp.Gettext, msgid)
#=> "Olá mundo"
While using functions from the Gettext
module yields the same results as
using macros (with the added benefit of dynamic arguments), all the
compile-time features mentioned in the previous section are lost.
Domains
The dgettext
and dngettext
functions/macros also accept a domain as one
of the arguments. The domain of a translation is determined by the name of the
PO file that contains that translation. For example, the domain of
translations in the it/LC_MESSAGES/errors.po
file is "errors"
, so those
translations would need to be retrieved with dgettext
or dngettext
:
MyApp.Gettext.dgettext "errors", "Error!"
#=> "Errore!"
When gettext
or ngettext
are used, the "default"
domain is used.
Interpolation
All *gettext
functions and macros provided by gettext support interpolation.
Interpolation keys can be placed in msgid
s or msgid_plural
s with by
enclosing them in %{
and }
, like this:
"This is an %{interpolated} string"
Interpolation bindings can be passed as an argument to all of the *gettext
functions/macros. For example, given the following PO file for the "it"
locale:
msgid "Hello, %{name}!"
msgstr "Ciao, %{name}!"
interpolation can be done like follows:
Gettext.put_locale MyApp.Gettext, "it"
MyApp.Gettext.gettext "Hello, %{name}!", name: "Meg"
#=> "Ciao, Meg!"
Interpolation keys that are in a string but not in the provided bindings
result in a Gettext.Error
exception:
MyApp.Gettext.gettext "Hello, %{name}!"
#=> ** (Gettext.Error) missing interpolation keys: name
Keys that are in the interpolation bindings but that don’t occur in the string are ignored. Interpolations in gettext are often expanded at compile time, ensuring a low performance cost when running them at runtime.
Pluralization
Pluralization in gettext for Elixir works very similar to how pluralization
works in GNU gettext. The *ngettext
functions/macros accept a msgid
, a
msgid_plural
and a count of elements; the right translation is chosen based
on the pluralization rule for the given locale.
For example, given the following snippet of PO file for the "it"
locale:
msgid "One error"
msgid_plural "%{count} errors"
msgstr[0] "Un errore"
msgstr[1] "%{count} errori"
the ngettext
macro can be used like this:
Gettext.put_locale MyApp.Gettext, "it"
MyApp.Gettext.ngettext "One error", "%{count} errors", 3
#=> "3 errori"
The %{count}
interpolation key is a special key since it gets replaced by
the number of elements argument passed to *ngettext
, like if the count: 3
key-value pair were in the interpolation bindings. Hence, never pass the
count
key in the bindings:
# `count: 4` is ignored here
MyApp.Gettext.ngettext "One error", "%{count} errors", 3, count: 4
#=> "3 errori"
You can specify a “pluralizer” module via the :plural_forms
option in the
configuration for each Gettext backend.
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app, plural_forms: MyApp.PluralForms
end
To learn more about pluralization rules, plural forms and what they mean to
Gettext check the documentation for Gettext.Plural
.
Missing translations
When a translation is missing in the specified locale (both with functions as well as with macros), the argument is returned:
- in case of calls to
gettext
/dgettext
, themsgid
argument is returned as is; - in case of calls to
ngettext
/dngettext
, themsgid
argument is returned in case of a singular value and themsgid_plural
is returned in case of a plural value (following the English pluralization rule).
For example:
Gettext.put_locale MyApp.Gettext, "foo"
MyApp.Gettext.gettext "Hey there"
#=> "Hey there"
MyApp.Gettext.ngettext "One error", "%{count} errors", 3
#=> "3 errors"
Empty translations
When a msgstr
is empty (""
), the translation is considered missing and the
behaviour described above for missing translation is applied. A plural
translation is considered to have an empty msgstr
if at least one
translation in the msgstr
is empty.
Contexts
The GNU Gettext implementation supports
contexts,
which are a way to “contextualize” translations. For example, in English, the
word “file” could be used both as a noun or as a verb. Contexts can be used to
solve similar problems: one could have a “imperative_verbs” context and a
“nouns” context as to avoid ambiguity. However, contexts increase the
complexity of Gettext and would increase the complexity of the implementation
of Gettext for Elixir, and for this reason we decided to not support them. The
problem they try to solve can still be solved just using domains: for example,
one could have the default-imperative_verbs
domain and the default-nouns
domain and use the d(n)gettext
family of macros/functions, and the final
result would be similar
Compile-time features
As mentioned above, using the gettext macros (as opposed to functions) allows
gettext to operate on those translations at compile-time. This can be used
to extract translations from the source code into POT files automatically
(instead of having to manually add translations to POT files when they’re added
to the source code). The gettext.extract
does exactly this: whenever there
are new translations in the source code, running gettext.extract
syncs the
existing POT files with the changed code base. Read the documentation for
Mix.Tasks.Gettext.Extract
for more information on the extraction process.
POT files are just template files and the translations in them do not actually contain translated strings. A POT file looks like this:
# The msgstr is empty
msgid "hello, world"
msgstr ""
Whenever a POT file changes, it’s likely that developers (or translators) will
want to update the corresponding PO files for each locale. To do that, gettext
provides the gettext.merge
Mix task. For example, running:
mix gettext.merge priv/gettext --locale pt_BR
will update all the PO files in priv/gettext/pt_BR/LC_MESSAGES
with the new
version of the POT files in priv/gettext
. Read more about the merging
process in the documentation for Mix.Tasks.Gettext.Merge
.
Finally, gettext is able to recompile modules that call use Gettext
whenever
PO files change. To enable this feature, the :gettext
compiler needs to be
added to the list of Mix compilers. In mix.exs
:
def project do
[compilers: [:gettext] ++ Mix.compilers]
end
Configuration
:gettext
configuration
The :gettext
application supports the following configuration options:
:default_locale
- a string which specifies the default global Gettext locale to use for all backends. See the “Locale” section for more information on backend-specific, global, and default locales.
Backend configuration
A Gettext backend supports some options to be configured. These options
can be configured in two ways: either by passing them to use Gettext
(hence
at compile time):
defmodule MyApp.Gettext do
use Gettext, options
end
or by using Mix configuration, configuring the key corresponding to the backend in the configuration for your application:
# For example, in config/config.exs
config :my_app, MyApp.Gettext, options
Note that the :otp_app
option (an atom representing an OTP application) has
to always be present and has to be passed to use Gettext
because it’s used
to determine the application to read the configuration of (:my_app
in the
example above); for this reason, :otp_app
can’t be configured via the Mix
configuration. This option is also used to determine the application’s
directory where to search translations in.
The following is a comprehensive list of supported options:
:priv
- a string representing a directory where translations will be searched. The directory is relative to the directory of the application specified by the:otp_app
option. It is recommended to always have this directory inside"priv"
, otherwise some features like the “mix compile.gettext” won’t work as expected. By default it’s"priv/gettext"
.:plural_forms
- a module which will act as a “pluralizer”. For more information, look at the documentation forGettext.Plural
.:default_locale
- a string which specifies the default locale to use for the given backend.:one_module_per_locale
- instead of bundling all locales into a single module, this option makes Gettext build one internal module per locale. This reduces compilation times and beam file sizes for large projects. This option requires Elixir v1.6.
Mix tasks configuration
You can configure Gettext Mix tasks under the :gettext
key in the
configuration returned by project/0
in mix.exs
:
def project() do
[app: :my_app,
# ...
gettext: [...]]
end
The following is a list of the supported configuration options:
:fuzzy_threshold
- the default threshold for the Jaro distance measuring the similarity of translations. Look at the documentation for themix gettext.merge
task (Mix.Tasks.Gettext.Merge
) for more information on fuzzy translations.:excluded_refs_from_purging
- a regex that is matched against translation references. Gettext will preserve all translations in all POT files that have a matching reference. You can use this pattern to prevent Gettext from removing translations that you have extracted using another tool.:compiler_po_wildcard
- a binary that specifies the wildcard that the:gettext
compiler will use to find changed PO files in order to recompile their respective Gettext backends. This wildcard has to be relative to the"priv"
directory of your application. Defaults to"gettext/*/LC_MESSAGES/*.po"
.:write_reference_comments
- a boolean that specifies whether reference comments should be written when outputting PO(T) files. If this isfalse
, reference comments will not be written when extracting translations or merging translations, and the ones already found in files will be discarded.
Link to this section Summary
Functions
Returns the translation of the given string in the given domain
Returns the pluralized translation of the given string in the given domain
Gets the global Gettext locale for the current process
Gets the locale for the current process and the given backend
Returns the translation of the given string in the "default"
domain
Returns all the locales for which PO files exist for the given backend
Returns the pluralized translation of the given string in the "default"
domain
Sets the global Gettext locale for the current process
Sets the locale for the current process and the given backend
Runs fun
with the global Gettext locale set to locale
Runs fun
with the gettext locale set to locale
for the given backend
Link to this section Types
Link to this section Functions
Returns the translation of the given string in the given domain.
The string is translated by the backend
module.
The translated string is interpolated based on the bindings
argument. For
more information on how interpolation works, refer to the documentation of the
Gettext
module.
If the translation for the given msgid
is not found, the msgid
(interpolated if necessary) is returned.
Examples
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app
end
Gettext.put_locale(MyApp.Gettext, "it")
Gettext.dgettext(MyApp.Gettext, "errors", "Invalid")
#=> "Non valido"
Gettext.dgettext(MyApp.Gettext, "errors", "%{name} is not a valid name", name: "Meg")
#=> "Meg non è un nome valido"
Gettext.dgettext(MyApp.Gettext, "alerts", "nonexisting")
#=> "nonexisting"
Returns the pluralized translation of the given string in the given domain.
The string is translated and pluralized by the backend
module.
The translated string is interpolated based on the bindings
argument. For
more information on how interpolation works, refer to the documentation of the
Gettext
module.
If the translation for the given msgid
and msgid_plural
is not found, the
msgid
or msgid_plural
(based on n
being singular or plural) is returned
(interpolated if necessary).
Examples
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app
end
Gettext.dngettext(MyApp.Gettext, "errors", "Error", "%{count} errors", 3)
#=> "3 errori"
Gettext.dngettext(MyApp.Gettext, "errors", "Error", "%{count} errors", 1)
#=> "Errore"
Gets the global Gettext locale for the current process.
This function returns the value of the global Gettext locale for the current
process. This global locale is shared between all Gettext backends; if you
want backend-specific locales, see get_locale/1
and put_locale/2
. If the
global Gettext locale is not set, this function returns the default global
locale (configurable in the configuration for the :gettext
application, see
the module documentation for more information).
Examples
Gettext.get_locale()
#=> "en"
Gets the locale for the current process and the given backend.
This function returns the value of the locale for the current process and the
given backend
. If there is no locale for the current process and the given
backend, then either the global Gettext locale (if set), or the default locale
for the given backend, or the global default locale is returned. See the
“Locale” section in the module documentation for more information.
Examples
Gettext.get_locale(MyApp.Gettext)
#=> "en"
Returns the translation of the given string in the "default"
domain.
Works exactly like:
Gettext.dgettext(backend, "default", msgid, bindings)
Returns all the locales for which PO files exist for the given backend
.
If the translations directory for the given backend doesn’t exist, then an empty list is returned.
Examples
With the following backend:
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app
end
and the following translations directory:
my_app/priv/gettext
├─ en
├─ it
└─ pt_BR
then:
Gettext.known_locales(MyApp.Gettext)
#=> ["en", "it", "pt_BR"]
Returns the pluralized translation of the given string in the "default"
domain.
Works exactly like:
Gettext.dngettext(backend, "default", msgid, msgid_plural, n, bindings)
Sets the global Gettext locale for the current process.
The locale is stored in the process dictionary. locale
must be a string; if
it’s not, an ArgumentError
exception is raised.
Examples
Gettext.put_locale("pt_BR")
#=> nil
Gettext.get_locale()
#=> "pt_BR"
Sets the locale for the current process and the given backend
.
The locale is stored in the process dictionary. locale
must be a string; if
it’s not, an ArgumentError
exception is raised.
Examples
Gettext.put_locale(MyApp.Gettext, "pt_BR")
#=> nil
Gettext.get_locale(MyApp.Gettext)
#=> "pt_BR"
with_locale(locale(), (() -> result)) :: result when result: var
Runs fun
with the global Gettext locale set to locale
.
This function just sets the global Gettext locale to locale
before running
fun
and sets it back to its previous value afterwards. Note that
put_locale/2
is used to set the locale, which is thus set only for the
current process (keep this in mind if you plan on spawning processes inside
fun
).
The value returned by this function is the return value of fun
.
Examples
Gettext.put_locale("fr")
MyApp.Gettext.gettext("Hello world")
#=> "Bonjour monde"
Gettext.with_locale "it", fn ->
MyApp.Gettext.gettext("Hello world")
end
#=> "Ciao mondo"
MyApp.Gettext.gettext("Hello world")
#=> "Bonjour monde"
Runs fun
with the gettext locale set to locale
for the given backend
.
This function just sets the Gettext locale for backend
to locale
before
running fun
and sets it back to its previous value afterwards. Note that
put_locale/2
is used to set the locale, which is thus set only for the
current process (keep this in mind if you plan on spawning processes inside
fun
).
The value returned by this function is the return value of fun
.
Examples
Gettext.put_locale(MyApp.Gettext, "fr")
MyApp.Gettext.gettext("Hello world")
#=> "Bonjour monde"
Gettext.with_locale MyApp.Gettext, "it", fn ->
MyApp.Gettext.gettext("Hello world")
end
#=> "Ciao mondo"
MyApp.Gettext.gettext("Hello world")
#=> "Bonjour monde"