Type-safe language translations in TypeScript

translation.ts

// We define a default master language and primary translation
// Types are extracted from that, and other translations must
// then conform to the primary translation.

const DANISH = {
    "Hello {name}!": "Hej {name}",
    "Welcome to the world": "Velkommen til Verden",
}

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",
} satisfies Language // 👈 type checking ✨

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

// EXAMPLES:
  
let t = translator(DANISH)

console.log(t("Hello {name}!", { name: "Joe" }))
console.log(t("Welcome to the world"))

t = translator(ENGLISH)

console.log(t("Hello {name}!", { name: "Joe" }))
console.log(t("Welcome to the world"))

t = translator(GERMAN)

console.log(t("Hello {name}!", { name: "Joe" }))
console.log(t("Welcome to the world"))

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