Dunno why you need that many slots, but of course you can exit the game and copy/move your saves to another place so you always have them.
If you are asking if there is an .ini or game edit to increase the number of save slots.....not that i know of......not without rewriting the core code.
You can't choose the folder Gothic saves games to, if that is why you want a folder called save 21.
However you can name the folder you store you saves in after you fill the maximum slots to whatever you want, I could be misunderstanding what your asking though.
i want a folder because i need more than 20 slots... but it seems i have to put them somewhere else... but do i have to copy what's inside the folder? or i can take the folder and put it in... let's say "Gothic 2 previous saves"
Well I would say move all your save games in your "Saves" directory to "Gothic 2 previous saves" but don't take the main folder with you, if you do make sure to create another "Saves" folder in your main Gothic directory for your new save games.
normally i would create a sub-folder and move the savegame folders into this new folder. later when i want to move newer savegames, i would rename the existing folders as not overwrite them with the newer ones.. or you can use a program like WinRAR or WinZip to compress the savegames and delete the folders.