Embedded manager

Use es-fluent-manager-embedded for general Rust applications, including CLIs, TUIs, desktop apps, and services. It compiles configured FTL resources into the binary and returns a cloneable EmbeddedI18n handle.

Add the dependency

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

Register package resources

Call the module macro from a library-reachable module:

// src/i18n.rs
pub use es_fluent_manager_embedded::EmbeddedI18n as I18n;

es_fluent_manager_embedded::define_i18n_module!();

// src/lib.rs
pub mod i18n;

In a workspace, call the macro in every package that owns FTL resources and link those owner crates into the host. One manager discovers the linked registrations; the host does not copy dependency FTL.

Initialize and localize

use es_fluent::EsFluent;
use es_fluent_manager_embedded::EmbeddedI18n;
use unic_langid::langid;

#[derive(EsFluent)]
struct Greeting<'a> {
    name: &'a str,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let i18n = EmbeddedI18n::try_new_with_language(langid!("en"))?;
    let text = i18n.localize_message(&Greeting { name: "Ada" });
    println!("{text}");
    Ok(())
}

When the initial language is not known at construction time, call EmbeddedI18n::try_new(), then select_language(...) before typed lookup.

Typed localize_message(...) and localize_label(...) treat a missing registered resource as a configuration error. The fallback locale is compile-time checked when es-fluent-build produces its catalog. Set missing_message_policy = "fallback-str" in the owning package’s i18n.toml to return snake_case source names from normal typed lookup instead. Import es_fluent::FluentLocalizerExt as _ and use try_localize_message(...) only at a boundary that handles the missing state. Labels provide a matching try_localize_label(...).

Select languages

select_language(...) succeeds when at least one application module can serve the requested locale and keeps supported modules active. Use select_language_strict(...) or try_new_with_language_strict(...) when every discovered application module must support the locale.

A failed switch keeps the previous ready locale. Cloned EmbeddedI18n handles share language state; construct a separate manager when independent locale state is required.

WASM debug builds embed locale assets automatically. For other debug targets that cannot read assets from the filesystem, enable the manager’s debug-embed feature.