Are The Sims 3 and The Sims Medieval creating a windows user folder structure on Installationspartition by anyone else on PC?

That looks this way
D:\Users\xxx\Documents\Electronic Arts\Die Sims Mittelalter\Screenshots

But the game creates no stuff in this folders and is saving screens into the folder from the documents directory. If I delete this folders, the games creating new ones.

I don't have multiple internal drives nor an install on a partition other than the one Windows is on, but yes I have heard of this happening. If you want your user game folders to be on D, usually the best procedure is to redirect the entire user Documents folder/library to D if you haven't already done that. Or use Junction Points. Can't give the exact (best) procedure for either at the moment, perhaps others here can, but there are all kinds of sites listing out the procedure for each version of Windows on the web. Usually players want to do the redirection somehow because C just isn't large enough to handle all that usage.

Or, if capacity on C isn't an issue and you are fine with the user game folder content really being on C with the phantom unused folders showing up on D, it's probably harmless.

Note that if C is a Solid State Drive (SSD) but D is a standard Hard Disk Drive (HDD), then you would lose any benefit you may be getting by having Documents on C. This isn't necessarily the case, it could even be the other way around, but small SSDs for Windows and much larger HDDs for most everything else would be a common configuration.

I did not changed anything. The games creating by their own this user folder on the installation partition(is not the same as the Windows that is installed on the SSD) and putting nothing into this folders. But it sounds more smart to change the parth for savegames to the HDD without Windows on the same partition.