howdy_i18n

Translations for howdy apps: ICU MessageFormat catalogues turned into typed Gleam functions, CLDR plural rules, and numbers, money, dates, relative times and lists written the way each locale writes them.

gleam add howdy_i18n@1

It depends on nothing else from Howdy, and runs on Erlang and JavaScript.

Messages

Write a catalogue per locale, locales/en.json:

{
  "greeting": "Hello, {name}!",
  "cart.items": "{count, plural, =0 {Your cart is empty} one {# item} other {# items}}"
}

and locales/de.json:

{
  "greeting": "Hallo, {name}!",
  "cart.items": "{count, plural, =0 {Ihr Warenkorb ist leer} one {# Artikel} other {# Artikel}}"
}

Generate a module with a function for each message:

gleam run -m howdy/i18n/cli -- gen

import howdy/i18n
import my_app/messages

let t = i18n.new("de")
messages.greeting(t, name: "Ada")    // "Hallo, Ada!"
messages.cart_items(t, count: 3)     // "3 Artikel"

A misspelt message, or a missing or wrongly typed argument, does not compile. gleam run -m howdy/i18n/cli -- check reports missing translations, plural forms a language needs but a message lacks, and invalid syntax, for CI.

Formatting

import howdy/i18n/format

format.integer(t, 1_234_567)                      // "1.234.567"
format.currency(t, minor: 123_456, code: "EUR")   // "1.234,56 €"
format.date(t, date, format.Long)                 // "19. Oktober 2026"
format.relative(t, -1, format.Day)                // "gestern"
format.list(t, ["Anna", "Ben", "Cem"])            // "Anna, Ben und Cem"

The data comes from CLDR 48 and covers 46 locales. scripts/cldr.mjs regenerates it from the pinned release.

Choosing the locale

Core’s howdy/locale negotiates a request’s locale from the URL, a cookie, a saved preference or accept-language. Pass its tag to i18n.new:

let t = i18n.new(locale.to_string(locale.detect(ctx, locales)))

See the internationalisation docs for the whole story, including Howdy’s own translated validation messages, UI components and auth pages.