This is TREMENDOUS!
I listen to mostly Classical Music these days, and that means lots of diacriticals in track names, artist names, album names, composer names, etc. So I have been searching for a solution to this problem for the better part of a year, including posting about it here last December. My only solution, until tonight, was to manually edit the copies of my macOS iTunes created playlists from within Rockbox - obviously extremely tedious - so I have made only a very few playlists that contain diacriticals. Now I am free of that limitation. Thank you so much.
Out of curiosity, and also hope, I tried running an m3u playlist through your app, but when I clicked on the 'Convert' button it didn't do anything. So I changed the playlist file's extension from .m3u to .m3u8 and tried again, and it worked! So that is a big bonus.
The pathname Find and Replace is also great, although I have easily dealt with that up until now by using a macOS app called TextMate which has a batch Find and Replace that allows the user to select a folder. But combining the diacriticals correction and pathname correction into a single step is a great convenience.
Again, thank you very much for providing this great service.