const l10n = {
  "ru": {
    "Language": "Язык",
    "Contacts": "Контакты"
  },
  "de": {
    "Language": "Sprache",
    "Contacts": "Kontakte"
  }
};

// ...

function useLocalize() {
  //ToDo: need cache?
  const language = useSelector(state => state.language);
  const l10nDict = useSelector(state => state.l10nDict[language]);

  return (!l10nDict)
    ? key => key
    : key => l10nDict[key] || key;
}