Will, thank you very much for answer. You are fast as always :-)
Kalileo, thank you! I found the post where you and Juanito were. It was about changing the values directly in the database. Actually, I use latest trunk of Userforms, and the problem is it's not creating any fields at all (not just incorrectly assigned id's)
I found a funny but simple way.
I created my form in the default language, added the fields, added the email recepients etc. Then I created a translation in my second language. Saved the page. Then in my _config.php, I changed the default locale. Flushed the site. I added fields on the translated form, made other changes. Saved it. Then switched back to my original locale =)
I know it's funny, but it worked..
So for people who will have the same problem,
Add your form as usual, then go to your _config_php file which is located under mysite folder. Change the lines below depending on your structure. In my example, I have Turkish (tr_TR) as second language.
Edit your form, which was not possible to edit before. And then switch back to old language settings in the _config.php file.
I don't think that i18n settings have any effect, just changing default locale is enough, but anyway I wrote them above, because I was lazy to try it one by one.