#localization #l10n #i18n #intl


High-level abstraction model for managing localization resources and runtime localization lifecycle

16 releases

0.7.0 Nov 9, 2022
0.6.0 Dec 17, 2021
0.5.0 Jul 8, 2021
0.4.0 Feb 9, 2021
0.0.2 Nov 26, 2019

#338 in Internationalization (i18n)

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1,806 downloads per month
Used in 3 crates


2.5K SLoC


fluent-fallback is a Rust implementation of the Project Fluent higher level API.

The Localization struct encapsulates a persistant localization context providing language fallbacking. The instance remains available throughout the whole life cycle of the corresponding UI, reacting to events such as locale changes, resource updates etc.

The API can be used directly, or can serve as an example of state manager for fluent-bundle and fluent-resmgr.

crates.io Build and test Coverage Status

Project Fluent keeps simple things simple and makes complex things possible. The syntax used for describing translations is easy to read and understand. At the same time it allows, when necessary, to represent complex concepts from natural languages like gender, plurals, conjugations, and others.



use fluent_fallback::Localization;

fn main() {
    // generate_messages is a closure that returns an iterator over FluentBundle
    // instances.
    let loc = Localization::new(vec!["simple.ftl".into()], generate_messages);

    let value = bundle.format_value("hello-world", None);

    assert_eq!(&value, "Hello, world!");


The implementation is in its early stages and supports only some of the Project Fluent's spec. Consult the list of milestones for more information about release planning and scope.

Local Development

cargo build
cargo test
cargo run --example simple-fallback

When submitting a PR please use cargo fmt (nightly).

Learn the FTL syntax

FTL is a localization file format used for describing translation resources. FTL stands for Fluent Translation List.

FTL is designed to be simple to read, but at the same time allows to represent complex concepts from natural languages like gender, plurals, conjugations, and others.

hello-user = Hello, { $username }!

Read the Fluent Syntax Guide in order to learn more about the syntax. If you're a tool author you may be interested in the formal EBNF grammar.

Get Involved

fluent-rs is open-source, licensed under the Apache License, Version 2.0. We encourage everyone to take a look at our code and we'll listen to your feedback.


We'd love to hear your thoughts on Project Fluent! Whether you're a localizer looking for a better way to express yourself in your language, or a developer trying to make your app localizable and multilingual, or a hacker looking for a project to contribute to, please do get in touch on the mailing list and the IRC channel.


~49K SLoC