Correct id3v2 tags can't be written in random codepages. For id3v2.3 it's either latin1 or utf16, id3v2.4 adds utf8 to the list.
If your tags are written by non-buggy software, you shouldn't have issues, unless you still use id3v1 (and if so, you should ask yourself why).
Apart from that, how would autodetection even work?