formatjs_intl

High-level Rust internationalization runtime. Owns message descriptors, translation catalogs, ICU4X locale negotiation, and shared compiled-message caching. Formatting delegates to formatjs_icu_messageformat.

message_descriptor! generates missing IDs with [sha512:contenthash:base64:10]. Pass id: to keep a semantic ID.

use formatjs_icu_messageformat::{Value, Values};
use formatjs_intl::{Intl, IntlCache, MessageCatalog, message_descriptor};
use std::{collections::HashMap, sync::Arc};

const TASKS: formatjs_intl::MessageDescriptor = message_descriptor!(
    id: "tasks.count",
    default_message: "{count, plural, one {# task} other {# tasks}}",
    description: "Task count"
);

let mut catalog = MessageCatalog::new();
catalog.insert(
    "fr",
    HashMap::from([(
        "tasks.count".to_owned(),
        "{count, plural, one {# tâche} other {# tâches}}".to_owned(),
    )]),
)?;
catalog.insert("en", HashMap::new())?;

let intl = Intl::try_new(
    ["fr-CA", "fr"],
    "en",
    Arc::new(catalog),
    Arc::new(IntlCache::new()),
)?;
let values: Values = HashMap::from([("count".to_owned(), Value::from(2_i64))]);
assert_eq!(intl.format_message_to_string(TASKS, &values)?, "2 tâches");
# Ok::<(), formatjs_intl::Error>(())

Message formatting falls back from the selected locale catalog to the default locale catalog, then the descriptor's default_message. Invalid translations also use this chain. Attach with_on_error to observe formatting errors while returning the fallback:

# use formatjs_intl::{FormatMessageError, Intl};
# fn configure(intl: Intl) -> Intl {
let intl = intl.with_on_error(|error: &FormatMessageError| {
    eprintln!("{error}");
});
# intl
# }

Precompile catalogs with the FormatJS CLI to skip runtime message parsing:

formatjs compile translations/fr.json --out-file translations/fr.compiled.json --ast

Add serde_json to load the compiled catalog:

[dependencies]
serde_json = "1"

# use formatjs_intl::{MessageCatalog, PrecompiledMessages};
let messages: PrecompiledMessages =
    serde_json::from_str(include_str!("../translations/fr.compiled.json"))?;
let mut catalog = MessageCatalog::new();
catalog.insert_precompiled("fr", messages)?;
# Ok::<(), Box<dyn std::error::Error>>(())

Precompiled messages are ready to format when inserted and do not use IntlCache.

Requested locales must already be ordered by preference. HTTP Accept-Language parsing stays in the application or web-framework adapter.

formatjs_intl 0.2.0

formatjs_intl