pascalfunction SetDefaultLang(Lang: string; Dir: string = ''; LocaleFileName: string = ''; ForceUpdate: boolean = true): string;
{ Arguments:
  Lang - language (e.g. 'ru', 'de', 'zh_CN'); empty argument is default language.
  Dir - custom translation files subdirectory (e.g. 'mylng'); empty argument means searching only in predefined subdirectories.
  LocaleFileName - custom translation file name; empty argument means that the name is the same as the one of executable.
  ForceUpdate - true means forcing immediate interface update. Only should be set to false when the procedure is
    called from unit Initialization section. User code normally should not specify it.
}
var
  lcfn: string;
  LocalTranslator: TUpdateTranslator;
  i: integer;

begin
  Result := '';
  LocalTranslator := nil;
  // search first po translation resources
  try
    lcfn := FindLocaleFileName('.po', Lang, Dir, LocaleFileName, Result);
    if lcfn <> '' then
    begin
      Translations.TranslateResourceStrings(lcfn);
      LocalTranslator := TPOTranslator.Create(lcfn);
    end
    else
    begin
      // try now with MO translation resources
      lcfn := FindLocaleFileName('.mo', Lang, Dir, LocaleFileName, Result);
      if lcfn <> '' then
      begin
        GetText.TranslateResourceStrings(UTF8ToSys(lcfn));
        LocalTranslator := TDefaultTranslator.Create(lcfn);
      end;
    end;
  except
    Result := '';
    lcfn := '';
  end;

  if lcfn<>'' then
    TranslateLCLResourceStrings(Lang, lcfn);

  if LocalTranslator<>nil then
  begin
    if Assigned(LRSTranslator) then
      LRSTranslator.Free;
    LRSTranslator := LocalTranslator;

    // Do not update the translations when this function is called from within
    // the unit initialization.
    if ForceUpdate=true then
    begin
      for i := 0 to Screen.CustomFormCount-1 do
        LocalTranslator.UpdateTranslation(Screen.CustomForms[i]);
      for i := 0 to Screen.DataModuleCount-1 do
        LocalTranslator.UpdateTranslation(Screen.DataModules[i]);
    end;
  end;
end;