Crate es_fluent_lang 

es-fluent-lang

Runtime support for es-fluent language management.

This crate provides the core language types (re-exporting unic-langid) and the optional “Language Enum” generator macro.

Features

#[es_fluent_language]

Generates a strongly-typed enum of all available languages in your project. It automatically scans your i18n.toml assets directory to find supported locales.

use es_fluent_lang::es_fluent_language;
use es_fluent::EsFluent;
use strum::EnumIter;

// Define an empty enum, and the macro fills it
#[es_fluent_language]
#[derive(Debug, Clone, Copy, PartialEq, Eq, EsFluent, EnumIter)]
pub enum Languages {}

If your assets_dir contains the same locales as the executable README example (en, fr-FR, and zh-CN), this generates:

pub enum Languages {
    En,
    FrFr,
    ZhCn,
}

It also implements:

• Default: Uses the fallback_language from your config.
• FromStr: Parses string codes (e.g., “en”, “fr-FR”, or “zh-CN”) into the enum variant.
• TryFrom<&LanguageIdentifier> / TryFrom<LanguageIdentifier>: Converts from a locale ID and returns an error for unsupported locales.
• Into<LanguageIdentifier>: Converts back to a standard locale ID.

For user-facing labels, derive EsFluent on the generated enum and call manager-backed localize_message(...) instead of relying on Display.

If you want to provide your own language-name translations, use #[es_fluent_language(custom)]. Custom mode skips the built-in es-fluent-lang runtime hook. When combined with #[derive(EsFluent)], it also leaves inventory registration enabled so your own FTL resources can provide the labels.

Feature Flags

• macros (default): Enables the #[es_fluent_language] macro.
• localized-langs: Format language names in the currently selected UI language instead of as autonyms.
• bevy: Backward-compatible feature for Bevy projects. The WASM force-link keepalive is no longer Bevy-specific.

Standard Translations

The crate also includes a built-in module for translating language names themselves (e.g., “English”, “Français”, “Deutsch”). This means you can easily build a “Language Picker” UI without manually translating the names of every language.

By default, labels are formatted directly from ICU4X display-name data as autonyms, so i18n.localize_message(&Languages::FrFr) resolves to français and i18n.localize_message(&Languages::ZhCn) resolves to 中文. With the localized-langs feature, the same ICU4X data is formatted in the currently selected UI language instead, so selecting English yields labels like French and Chinese.

For a language picker, iterate your generated enum, render each label through the active manager, and pass the selected variant back to the manager:

use es_fluent::FluentMessage as _;
use strum::IntoEnumIterator as _;

for language in Languages::iter() {
    let label = i18n.localize_message(&language);
    println!("{language:?}: {label}");
}

i18n.select_language(Languages::FrFr)?;

The runtime resolves fallback locales through the shared ICU4X/CLDR fallback chain when a display locale is missing exact display-name data. If you need fully custom labels for project-specific or unsupported locale tags, use #[es_fluent_language(custom)] and ship your own translations.

The built-in language-name module follows successful manager locale switches but does not count as application content support. A manager still reports an unsupported locale when no application translation module can serve it.

For wasm32 builds, default #[es_fluent_language] enums emit a small force-link keepalive hook so the built-in language-name module is retained across managers, including Dioxus and Bevy.

Macros

langid

Structs

LanguageIdentifier

LanguageIdentifier is a core struct representing a Unicode Language Identifier.

Attribute Macros

es_fluent_language

Attribute macro that expands a language enum based on the i18n.toml configuration. Which generates variants for each language in the i18n folder structure.