code: public void setL10N(String locale, String language) {
      try {
        JSONObject plistJSON = getPreferenceFile(locale, language);
        writeOnDisk(plistJSON, globalPreferencePlist);
      } catch (Exception e) {
        throw new WebDriverException("cannot configure simulator", e);
      }
    }
docs: set the emulator to the given locale.Required a clean context (can only be done after "reset
  content and settings" )
  
  @param locale   fr_FR
  @param language fr