MessageFormat2 messages, formatted in Rust.

#Pick the plural form for the language

A matcher lists variants by key. 0 is an exact number, one and few are the language’s plural categories, and * is the fallback every matcher needs.

use dxn_i18n::{Args, Message};
use dxn_intl::parse_locale;

let message = Message::parse(
    ".input {$count :number}
     .match $count
     0   {{Your cart is empty.}}
     one {{One item in your cart.}}
     *   {{{$count} items in your cart.}}",
)?;
let en = parse_locale("en")?;
assert_eq!(message.format(&en, &Args::new().with("count", 1200)), "1,200 items in your cart.");

See Selecting variants for ordinals, text keys and several selectors.

#Format in the user’s locale and preferences

The locale carries the user’s region and Unicode extensions. A de-CH user sees Swiss separators in a de message, and -u-hc-h23 turns every time into a 24-hour one.

use dxn_i18n::{Args, Bundle, Translator};
use dxn_intl::{DateTime, parse_locale};

let mut translator = Translator::new(parse_locale("en")?);
for (tag, json) in [("en", r#"{ "at": "At {$t :time}." }"#), ("de", r#"{ "price": "{$p :number}" }"#)] {
    let mut bundle = Bundle::new(parse_locale(tag)?);
    bundle.add_json(json)?;
    translator.add_bundle(bundle);
}

translator.set_locale(parse_locale("de-CH")?);
assert_eq!(translator.format("price", &Args::new().with("p", 1234.5)), "1'234.5");

translator.set_locale(parse_locale("en-US-u-hc-h23")?);
let at = Args::new().with("t", DateTime::new(2026, 10, 27, 15, 45, 0)?);
assert_eq!(translator.format("at", &at), "At 15:45.");

See The Translator for the lookup chain and Dates and times.

#Render markup without string surgery

Translators put {#link} where the link belongs in their language. format_to_parts gives you the pieces, with markup options resolved.

use dxn_i18n::{Args, Bundle, Translator};
use dxn_intl::parse_locale;

let mut en = Bundle::new(parse_locale("en")?);
en.add("terms", "Read the {#link href=$url}terms{/link} first.")?;
let mut translator = Translator::new(parse_locale("en")?);
translator.add_bundle(en);

let args = Args::new().with("url", "https://example.com/terms");
let parts = translator.format_to_parts("terms", &args).expect("the message exists").text;
assert_eq!(parts.len(), 5);
// [Text("Read the "), Markup { kind: Open, name: "link", options: [("href", ..)] },
//  Text("terms"), Markup { kind: Close, name: "link", .. }, Text(" first.")]

See Markup and parts for a renderer.

#Errors that stay on screen

Formatting never panics and never returns nothing. What cannot be resolved shows as a fallback, and the errors come back next to the text.

use dxn_i18n::{Args, FormatError, Message, MessageFormatter};
use dxn_intl::parse_locale;

let message = Message::parse("Hello {$name}, you have {$n :number} messages.")?;
let formatter = MessageFormatter::new(parse_locale("en")?);
let formatted = formatter.format(&message, &Args::new().with("n", "many"));

assert_eq!(formatted.text, "Hello {$name}, you have {$n} messages.");
assert_eq!(formatted.errors[0], FormatError::UnresolvedVariable("name".to_string()));

See Errors and fallbacks.

#Add your own function

A function is a plain fn that returns a value able to format itself and, if you like, to select a variant. Register it under a namespace.

use std::sync::Arc;
use dxn_i18n::{
    Args, FunctionContext, FunctionError, FunctionRegistry, Message, MessageFormatter, Options,
    ResolvedValue, TextValue, Value,
};
use dxn_intl::parse_locale;

fn shout(
    _: &mut FunctionContext<'_>,
    operand: Option<&Value>,
    _: &Options,
) -> Result<Arc<dyn ResolvedValue>, FunctionError> {
    let text = operand.and_then(Value::as_str).unwrap_or_default();
    Ok(Arc::new(TextValue(text.to_uppercase())))
}

let mut functions = FunctionRegistry::default();
functions.register("my:shout", shout);
let formatter = MessageFormatter::new(parse_locale("en")?).with_functions(Arc::new(functions));
let message = Message::parse("Welcome, {$name :my:shout}!")?;
assert_eq!(formatter.format(&message, &Args::new().with("name", "ana")).text, "Welcome, ANA!");

See Custom functions.