Note: non-ascii characters have indeed been widespread for a long time, but here's an example: if you get a bunch of attached files in Yahoo mail and choose a bulk download, yahoo zips them up for you. Then you unzip the file and find that the non-ascii characters have been corrupted.
Yahoo is probably the second or third biggest email provider in the world and they don't support non-ascii characters... I think I can get away with doing the same in my hobby project, even though I did attempt to one-up them.

Spaces are less of an issue. I personally think it's not a good idea to use spaces in a filename, but they don't seem to cause a problem in the aligner.