decap-missing-lang.ts

const objToKeysDeep = (obj: object, prefix = ""): string[] =>
  Object.entries(obj).flatMap(([key, value]) =>
    typeof value === "object"
      ? objToKeysDeep(value, `${prefix}${key}.`)
      : `${prefix}${key}`
  );

const missingInLang = async (lang: string) => {
  const en = (await import(`./packages/decap-cms-locales/src/en/index.js`))
    .default;
  const transl = (
    await import(`./packages/decap-cms-locales/src/${lang}/index.js`)
  ).default;
  return new Set(objToKeysDeep(en)).difference(new Set(objToKeysDeep(transl)));
};

console.log(await missingInLang("cs"));