wekan/client/lib/i18n.js

import { TAPi18n } from '/imports/i18n';

// We save the user language preference in the user profile, and use that to set
// the language reactively. If the user is not connected we use the language
// information provided by the browser, and default to english.

Meteor.startup(() => {
  const currentUser = Meteor.user();
  // Select first available language
  const [language] = [
    // User profile
    currentUser?.profile?.language,
    // Browser locale
    navigator.languages?.at(0),
    navigator.language,
    navigator.userLanguage,
  ].filter(Boolean);
  if (language) {
    TAPi18n.setLanguage(language);
  }
});