Type-safe language translations in TypeScript

translation.ts

const DANISH = {
    "Hello {{name}}!": "Hej {{name}}",
    "Welcome to the world": "Velkommen til Verden",
    "You have {{amount}} {{cookies}}": "Du har {{amount}} {{cookies}}",
    "cookie": "kage",
    "cookies": "kager",
    "Missing translation": "Manglende oversættelse",
}

type TranslationKey = keyof typeof DANISH

type Language = Record<TranslationKey, string>

const ENGLISH = {} as Language

const GERMAN = {
    "Hello {{name}}!": "Hallo {{name}}",
    "Welcome to the world": "Willkommen in Der Welt",
    "You have {{amount}} {{cookies}}": "Du hast {{amount}} {{cookies}}",
    "cookie": "kuche",
    "cookies": "kuchen"
} satisfies Language // 👈 type checking ✨

const translator = (lang: Language) =>
    (key: TranslationKey, values: Record<string, string|{ toString(): string }> = {}) =>
        (lang[key] || key).replace(/{{([^{}}]+)}}/g, (match, key) => String(key in values ? values[key] : match))

// EXAMPLES:
  
let numCookies = 1

for (const language of [DANISH,ENGLISH,GERMAN]) {
    const t = translator(language)

    console.log(t("Hello {{name}}!", { name: "Joe" }))
    console.log(t("Welcome to the world"))
    console.log(t("You have {{amount}} {{cookies}}", { amount: numCookies, cookies: numCookies === 1 ? t("cookie") : t("cookies") }))

    numCookies += 1
}

const t = translator(DANISH)

console.log(t("This message is undefined")) // 👈 type checking ✨