phanpy/src/utils/get-translate-target-language.js

import translationTargetLanguages from '../data/lingva-target-languages';

import localeMatch from './locale-match';
import mem from './mem';
import states from './states';

const locales = mem(() => [
  new Intl.DateTimeFormat().resolvedOptions().locale,
  ...navigator.languages,
]);

const localeTargetLanguages = () =>
  localeMatch(
    locales(),
    translationTargetLanguages.map((l) => l.code.replace('_', '-')), // The underscore will fail Intl.Locale inside `match`
    'en',
  );

function getTranslateTargetLanguage(fromSettings = false) {
  if (fromSettings) {
    const { contentTranslationTargetLanguage } = states.settings;
    if (contentTranslationTargetLanguage) {
      return contentTranslationTargetLanguage;
    }
  }
  return localeTargetLanguages();
}

export default getTranslateTargetLanguage;