Bevy manager

Use es-fluent-manager-bevy to connect typed messages to Bevy ECS, assets, and reactive UI text.

Add the manager

[dependencies]
bevy = "0.19"
es-fluent = "0.18"
es-fluent-manager-bevy = "0.19"
unic-langid = "0.9"

// src/i18n.rs
es_fluent_manager_bevy::define_i18n_module!();

Install the plugin

use bevy::prelude::*;
use es_fluent_manager_bevy::I18nPlugin;
use unic_langid::langid;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins(I18nPlugin::with_language(langid!("en")))
        .run();
}

Generated manager modules contribute their configured resources. Link every owner library in a multi-crate application; the host does not copy dependency FTL.

Fallback-locale message values are compile-time checked through es-fluent-build. Set missing_message_policy = "fallback-str" in the owning package’s i18n.toml when BevyI18n and FluentText<T> should render snake_case source names after locale fallback is exhausted.

Localize UI text

Derive BevyFluentText for component types that should refresh when the locale changes, then wrap values in FluentText<T>:

use bevy::prelude::*;
use es_fluent::EsFluent;
use es_fluent_manager_bevy::{BevyFluentText, FluentText};

#[derive(BevyFluentText, Clone, Component, EsFluent)]
enum UiMessage {
    StartGame,
    Settings,
}

fn spawn_menu(mut commands: Commands) {
    commands.spawn((
        FluentText::new(UiMessage::StartGame),
        Text::new(""),
    ));
}

Only a type used directly as FluentText<T> needs registration. Nested message fields are formatted when the parent value refreshes.

If a named struct field or named enum variant field depends on the requested locale, mark it with #[locale]. Its type must implement TryFrom<&LanguageIdentifier>. The derive generates locale refresh behavior and registration.

For an external type that cannot derive BevyFluentText, register it manually with register_fluent_text::<T>().

Localize in systems

Request BevyI18n as a system parameter:

use es_fluent_manager_bevy::BevyI18n;

fn update_title(i18n: BevyI18n) {
    let title = i18n.localize_message(&UiMessage::Settings);
    // Apply the title to application state.
    let _ = title;
}

Use RequestedLanguageId for the latest user request and ActiveLanguageId for the published locale. Failed asset reloads or locale switches keep the last accepted locale active.

Order application systems

The plugin labels localization phases with I18nSet. Use Bevy’s .before(...) and .after(...) APIs when an application system must run around locale synchronization or text refresh:

use bevy::prelude::*;
use es_fluent_manager_bevy::I18nSet;

fn persist_locale() {}
fn update_window_title() {}

app.add_systems(Update, persist_locale.after(I18nSet::LocaleSync));
app.add_systems(PostUpdate, update_window_title.after(I18nSet::TextUpdate));