I have Mac OS X and iTunes 10.2.2, and several m3u files (standard, non extended) containing the paths to songs that are already in the library, just not organized into playlists. I ran a Python script over the m3u playlists to check if each song exists, and verified a few of them by hand: they're all there, and at the correct paths.
When I open iTunes, then go to File -> Library -> Import Playlist and import the m3u files, only tracks without special characters in the name will show up.
For example: if I have a playlist with ten tracks, where one of them, say
/Users/myname/Music/Library/Glen Hansard and Markéta Irglová/The Swell Season/03 - Falling Slowly.mp3, uses accent marks, like ü, ñ, or é, or anything not resembling something I could type without using Alt+ on a standard EN-US keyboard, it doesn't show up. All the other tracks in the playlist show fine, just not the "odd" ones.
If I copy and paste the file path of an "odd" song out of the m3u file and into Terminal and run
open on it, it opens in iTunes just fine, and is recognized as already being present in my library.
There are too many playlists and songs (more than 100,000) for me to go through and manually fix all of the names, and it's not even my library to begin with. Are there any solutions to this, or any workarounds? Perhaps something involving the type of UTF iTunes likes to see versus the kind that's being passed to it in the m3u files?