Crate i18n_embed
source ·Expand description
Traits and macros to conveniently embed localization assets into your application binary or library in order to localize it at runtime. Works in unison with cargo-i18n.
This library recommends tha you make use of
rust-embed to perform the
actual embedding of the language files, unfortunately using this
currently requires you to manually add it as a dependency to your
project and implement its trait on your struct in addition to
I18nAssets. RustEmbed
will not compile if the
target folder
path is invalid, so it is recommended to either
run cargo i18n
before building your project, or committing the
localization assets into source control to ensure that the the
folder exists and project can build without requiring cargo i18n
.
§Optional Features
The i18n-embed
crate has the following optional Cargo features:
rust-embed
(Enabled by default)- Enable an automatic implementation of I18nAssets for any
type that also implements
RustEmbed
.
- Enable an automatic implementation of I18nAssets for any
type that also implements
fluent-system
- Enable support for the
fluent localization system
via the
fluent::FluentLanguageLoader
in this crate.
- Enable support for the
fluent localization system
via the
gettext-system
- Enable support for the
gettext localization
system using the tr macro and
the gettext crate
via the
gettext::GettextLanguageLoader
in this crate.
- Enable support for the
gettext localization
system using the tr macro and
the gettext crate
via the
desktop-requester
- Enables a convenience implementation of LanguageRequester trait called `DesktopLanguageRequester for the desktop platform (windows, mac, linux), which makes use of the locale_config crate for resolving the current system locale.
web-sys-requester
- Enables a convenience implementation of
LanguageRequester trait called
WebLanguageRequester
which makes use of the web-sys crate for resolving the language being requested by the user’s web browser in a WASM context.
- Enables a convenience implementation of
LanguageRequester trait called
§Examples
§Fluent Localization System
The following is a simple example for how to localize your binary
using this library when it first runs, using the fluent
localization system, directly instantiating the
FluentLanguageLoader
.
First you’ll need the following features enabled in your
Cargo.toml
:
[dependencies]
i18n-embed = { version = "VERSION", features = ["fluent-system", "desktop-requester"]}
rust-embed = "8"
Set up a minimal i18n.toml
in your crate root to use with
cargo-i18n
(see cargo
i18n
for more information on the configuration file format):
# (Required) The language identifier of the language used in the
# source code for gettext system, and the primary fallback language
# (for which all strings must be present) when using the fluent
# system.
fallback_language = "en-GB"
# Use the fluent localization system.
[fluent]
# (Required) The path to the assets directory.
# The paths inside the assets directory should be structured like so:
# `assets_dir/{language}/{domain}.ftl`
assets_dir = "i18n"
Next, you want to create your localization resources, per language
fluent (.ftl
) files. language
needs to conform to the Unicode
Language
Identifier
standard, and will be parsed via the unic_langid
crate:
my_crate/
Cargo.toml
i18n.toml
src/
i18n/
{language}/
{domain}.ftl
Then in your Rust code:
use i18n_embed::{DesktopLanguageRequester, fluent::{
FluentLanguageLoader, fluent_language_loader
}};
use rust_embed::RustEmbed;
#[derive(RustEmbed)]
#[folder = "i18n"] // path to the compiled localization resources
struct Localizations;
fn main() {
let language_loader: FluentLanguageLoader = fluent_language_loader!();
// Use the language requester for the desktop platform (linux, windows, mac).
// There is also a requester available for the web-sys WASM platform called
// WebLanguageRequester, or you can implement your own.
let requested_languages = DesktopLanguageRequester::requested_languages();
let _result = i18n_embed::select(
&language_loader, &Localizations, &requested_languages);
// continue on with your application
}
To access localizations, you can use FluentLanguageLoader
’s
methods directly, or, for added compile-time checks/safety, you
can use the fl!() macro.
Having an i18n.toml
configuration file enables you to do the
following:
- Use the cargo i18n tool to perform validity checks (not yet implemented).
- Integrate with a code-base using the
gettext
localization system. - Use the
fluent::fluent_language_loader!()
macro to pull the configuration in at compile time to create thefluent::FluentLanguageLoader
. - Use the fl!() macro to have added compile-time safety when accessing messages.
§Gettext Localization System
The following is a simple example for how to localize your binary
using this library when it first runs, using the gettext
localization system. Please note that the gettext
localization
system is technically inferior to fluent
in a number of
ways,
however there are always legacy reasons, and the
developer/translator ecosystem around gettext
is mature.
The gettext::GettextLanguageLoader
in this example is
instantiated using the gettext::gettext_language_loader!()
macro, which automatically determines the correct module for the
crate, and pulls settings in from the i18n.toml
configuration
file.
First you’ll need the following features enabled in your
Cargo.toml
:
[dependencies]
i18n-embed = { version = "VERSION", features = ["gettext-system", "desktop-requester"]}
rust-embed = "8"
Set up a minimal i18n.toml
in your crate root to use with
cargo-i18n
(see cargo
i18n
for more information on the configuration file format):
# (Required) The language identifier of the language used in the
# source code for gettext system, and the primary fallback language
# (for which all strings must be present) when using the fluent
# system.
fallback_language = "en"
# Use the gettext localization system.
[gettext]
# (Required) The languages that the software will be translated into.
target_languages = ["es"]
# (Required) Path to the output directory, relative to `i18n.toml` of
# the crate being localized.
output_dir = "i18n"
Install and run cargo i18n
for your crate to generate the language specific po
and mo
files, ready to be translated. It is recommended to add the
i18n/pot
folder to your repository gitignore.
Then in your Rust code:
use i18n_embed::{DesktopLanguageRequester, gettext::{
gettext_language_loader
}};
use rust_embed::RustEmbed;
#[derive(RustEmbed)]
// path to the compiled localization resources,
// as determined by i18n.toml settings
#[folder = "i18n/mo"]
struct Localizations;
fn main() {
// Create the GettextLanguageLoader, pulling in settings from `i18n.toml`
// at compile time using the macro.
let language_loader = gettext_language_loader!();
// Use the language requester for the desktop platform (linux, windows, mac).
// There is also a requester available for the web-sys WASM platform called
// WebLanguageRequester, or you can implement your own.
let requested_languages = DesktopLanguageRequester::requested_languages();
let _result = i18n_embed::select(
&language_loader, &Localizations, &requested_languages);
// continue on with your application
}
§Automatic Updating Selection
Depending on the platform, you can also make use of the LanguageRequester’s ability to monitor changes to the currently requested language, and automatically update the selected language using a Localizer:
use std::sync::Arc;
use i18n_embed::{
DesktopLanguageRequester, LanguageRequester,
DefaultLocalizer, Localizer, fluent::FluentLanguageLoader
};
use rust_embed::RustEmbed; use lazy_static::lazy_static;
use unic_langid::LanguageIdentifier;
#[derive(RustEmbed)]
#[folder = "i18n/ftl"] // path to localization resources
struct Localizations;
lazy_static! {
static ref LANGUAGE_LOADER: FluentLanguageLoader = {
// Usually you could use the fluent_language_loader!() macro
// to pull values from i18n.toml configuration and current
// module here at compile time, but instantiating the loader
// manually here instead so the example compiles.
let fallback: LanguageIdentifier = "en-US".parse().unwrap();
FluentLanguageLoader::new("test", fallback)
};
}
fn main() {
let localizer = DefaultLocalizer::new(&*LANGUAGE_LOADER, &Localizations);
let localizer_arc: Arc<dyn Localizer> = Arc::new(localizer);
let mut language_requester = DesktopLanguageRequester::new();
language_requester.add_listener(Arc::downgrade(&localizer_arc));
// Manually check the currently requested system language,
// and update the listeners. NOTE: Support for this across systems
// currently varies, it may not change when the system requested
// language changes during runtime without restarting your application.
// In the future some platforms may also gain support for
// automatic triggering when the requested display language changes.
language_requester.poll().unwrap();
// continue on with your application
}
The above example makes use of the
DefaultLocalizer, but you can also implement
the Localizer trait yourself for a custom solution.
It also makes use of
lazy_static to allow the
LanguageLoader implementation to be stored
statically, because its constructor is not const
.
§Localizing Libraries
If you wish to create a localizable library using i18n-embed
,
you can follow this code pattern in the library itself:
use std::sync::Arc;
use i18n_embed::{
DefaultLocalizer, Localizer, LanguageLoader,
fluent::{
fluent_language_loader, FluentLanguageLoader
}};
use rust_embed::RustEmbed; use lazy_static::lazy_static;
#[derive(RustEmbed)]
#[folder = "i18n/mo"] // path to the compiled localization resources
struct Localizations;
lazy_static! {
static ref LANGUAGE_LOADER: FluentLanguageLoader = {
let loader = fluent_language_loader!();
// Load the fallback langauge by default so that users of the
// library don't need to if they don't care about localization.
// This isn't required for the `gettext` localization system.
loader.load_fallback_language(&Localizations)
.expect("Error while loading fallback language");
loader
};
}
// Get the `Localizer` to be used for localizing this library.
pub fn localizer() -> Arc<dyn Localizer> {
Arc::new(DefaultLocalizer::new(&*LANGUAGE_LOADER, &Localizations))
}
People using this library can call localize()
to obtain a
Localizer, and add this as a listener to their chosen
LanguageRequester.
§Localizing Sub-crates
If you want to localize a sub-crate in your project, and want to extract strings from this sub-crate and store/embed them in one location in the parent crate, you can use the following pattern for the library:
use std::sync::Arc;
use i18n_embed::{
DefaultLocalizer, Localizer, gettext::{
gettext_language_loader, GettextLanguageLoader
}};
use i18n_embed::I18nAssets;
use lazy_static::lazy_static;
lazy_static! {
static ref LANGUAGE_LOADER: GettextLanguageLoader =
gettext_language_loader!();
}
/// Get the `Localizer` to be used for localizing this library,
/// using the provided embedded source of language files `embed`.
pub fn localizer<'a>(embed: &'a (dyn I18nAssets + Send + Sync + 'static)) -> Arc<dyn Localizer + 'a> {
Arc::new(DefaultLocalizer::new(
&*LANGUAGE_LOADER,
embed
))
}
For the above example, you can enable the following options in the
sub-crate’s i18n.toml
to ensure that the localization resources
are extracted and merged with the parent crate’s pot
file:
# ...
[gettext]
# ...
# (Optional) If this crate is being localized as a subcrate, store the final
# localization artifacts (the module pot and mo files) with the parent crate's
# output. Currently crates which contain subcrates with duplicate names are not
# supported.
extract_to_parent = true
# (Optional) If a subcrate has extract_to_parent set to true, then merge the
# output pot file of that subcrate into this crate's pot file.
collate_extracted_subcrates = true
Re-exports§
pub use unic_langid;
Modules§
- This module contains the types and functions to interact with the
fluent
localization system. - This module contains the types and functions to interact with the
gettext
localization system.
Structs§
- A way to multiplex implmentations of
I18nAssets
. - A simple default implemenation of the Localizer trait.
- A LanguageRequester for the desktop platform, supporting windows, linux and mac. It uses locale_config to select the language based on the system selected language.
- An I18nAssets implementation which pulls assets from the OS file system.
- Provide the functionality for overrides and listeners for a LanguageRequester implementation.
- A language resource file, and its associated
language
. - An error that occurs during notification of changes when the
autoreload feature is enabled.
- A wrapper for
rust_embed::RustEmbed
that supports notifications when files have changed on the file system. A wrapper is required to providebase_dir
as this is unavailable in the type derived by therust_embed::RustEmbed
macro. - A LanguageRequester for the
web-sys
web platform.
Enums§
- An error that occurs in this library.
Traits§
- A trait to handle the retrieval of localization assets.
- A trait used by I18nAssets to load a language file for a specific rust module using a specific localization system. The trait is designed such that the loader could be swapped during runtime, or contain state if required.
- A trait used by I18nAssets to ascertain which languages are being requested.
- This trait provides dynamic access to an LanguageLoader and an I18nAssets, which are used together to localize a library/crate on demand.
- An entity that watches for changes to localization resources.
Functions§
- Get the translation domain from the module path (first module in the module path).
- Select the most suitable available language in order of preference by
requested_languages
, and load it using the provided LanguageLoader from the languages available in I18nAssets. Returns the available languages that were negotiated as being the most suitable to be selected, and were loaded by LanguageLoader::load_languages(). If there were no available languages, then no languages will be loaded and the returnedVec
will be empty.