Lanux, using the Quicktagger component for Foobar2000 (there will be other tagging, etc apps that'll let you do the same) you can create custom tags and add pretty much any kind of info to them. I've made tags for tempo and personal rating, for instance. I wouldn't want to have a separate tag for languages, everything non-English goes into the 'World' genre but you can add sub-genres to the main genre itself, Eg: "World / Portuguese."
Foo supports auto-playlists - Eg: I can have an auto-playlist for (pseudocode -->) Genre=Electronic & Tempo>4 & Personal Rating>=3 & whatever other criteria, which could be something like 'Genre HAS Portuguese' (though that wouldn't get me too many matches in 'Electronic'
) Any song that matches the criteria will be added to the playlist on the fly.
I tried a few media library apps a couple of months back before I realised Foo was one of the fastest + most powerful tools for the job.
Edit: You can also display any custom tag info in its own column so sorting on any field is as easy as clicking on a column header - and you can do cool stuff like start with the slow stuff and pick up pace, more info that you asked for but, whatever!
