Incorrect handling of multibyte characters

There is a bug that prevent using filenames with multibyte characters in upload.module. For example, attaching file with russian filename with spaces, result in lost of first word. Also, it's not possible to download such files in some browsers because of national characters in url.
Quick look to module source reveal that all string functions are not unicode aware (however, there are drupal wrappers existing for some of them, like drupal_strlen, drupal_strtoupper and drupal_strtolower). I think, this is odd for core module.
I think, the solution may be replacing all string functions with their unicode equivalents and using urlencode() to encode urls with national characters.