Repair encoding of ID3 tags

"You want Ex Falso, the tag editor included in the Quod Libet project. Picard (the MusicBrainz tagger) may use the same tagging library, but QL originated it.

In particular, you want the Mutagen tagging library, which supports id3v2.4 (and by ""support"" I mean ""enforce"" ...militarily...). It is also excellent with character encodings, and includes a basic scriptable commandline tagger (mid3v2). As far as your normalization step goes, Mutagen only saves tags in ID3v2.4. It is certainly capable of converting all text into UTF-8, but you may need to script that yourself (I believe that the mid3v2 tool's defaults are to keep the current encoding where possible, and I don't know if it can be told to save everything in a particular encoding). Mutagen is written in Python.

Ex Falso is a nice, clean GUI , and supports most of the major retag-multiple-files features you'd expect. I don't think it does much in the way of internet lookups and I don't know how it is with album artwork -- Quod Libet may support that; Ex Falso can do it with a plugin, should one exist, though one might not exist. I've never needed that functionality -- I use EF and mid3v2 in concert to handle my retagging needs."

"How about Mp3Tag with Wine?
Features (among others):

Batch Tag Editing Write ID3v1.1, ID3v2.3, ID3v2.4, MP4, WMA, APEv2 Tags and Vorbis Comments to multiple files at once.
Import from Amazon, discogs, freedb, MusicBrainz Save typing and import tags from online databases like Amazon, discogs, freedb, MusicBrainz, and more.
Replace characters or words Replace strings in tags and filenames (with support for Regular Expressions).
Full Unicode Support User-interface and tagging are fully Unicode compliant."