If the field contents of the normal and the sort field are the same, then you can spare the effort as then the player would not sort the files differently.
Could you give an example in which you entered different strings in the normal and the sort field and the sorting result was not as you expected?
Or to cut this a little short: MP3tag serves the ID3 standard for MP3 files. Modifications in treating charactersets are vain and void if the players don't follow suit (and the standard gets updated).
So actually, I doubt that there are really problems in respect to the character sets.