I was reading in the reviews that the languages from the retail version were not included. I am happy to inform you that it is included as well as several others that were not mentioned on the GOG site page. Following is a shot of the Language Setup.exe found in the SimCity 4 directory.

Nice. Polish language version is available. :D

Thanks for the info!

I'm also happy that Polish language is included.

Out of interest, what is the default language? English or English UK? Reason I ask is that I'm interested in finding out if the regional settings also get changed by this, such as American (mm/dd/yyyy) and English (dd/mm/yyyy) date formats, or whether these are bound to the regional version of the game itself.

Just as a side note, if you're using Win7/Win8, you need to execute that language selector launcher with admin rights, or it won't work, it'll have the selection sticked, but it doesn't change anything in the game itself! I had such a problem, and it was that...