code: async function setPreferredMcpLanguage(accessToken, languageCode) {
      let language = getValidLanguageOrThrow(languageCode);
  
      let currentLanguages = await getPreferredMcpLanguages(accessToken);
  
      return mcpCustomizr.putSettings(accessToken, {
          language: updatePreferredLanguage(language, currentLanguages),
      });
  }
docs: Update the preferred language in Customizr
  @param {string} accessToken - Access token to use to call Customizr
  @param {string} languageCode - ISO-639 language code (eg. bul, en, eng, de)
  @return {Promise<void>}