Thank you. For your information: this is for a script that will be used on Windows, Linux and Mac. It seems to have no problem with non-ASCII filenames in Linux (Ubuntu, anyway), but it fails in Windows and Mac OS X.
If it doesn't require too many changes, I'd like to make it work with non-ASCII characters on Windows, but it's not critically important. If you can give me a simple step by step on how to make it work, I'll be grateful. Otherwise, I can always warn users to rename their files.