You can reload a file using a different encoding if Vim was not able to detect
the correct encoding:
:e ++enc=<encoding>


When you load a file with box drawing characters in it and those characters
render incorrect as A-umlauts (Ä) or other things, here is a list of
codepages/encodings you can try:

cp850
cp860
cp1252
windows-1252
iso-8859-1

see http://skeena.net/kb/character-sets.html for a much longer list


If you've got chinese characters, you've probably got a unicode file in the wrong mode:

utf-16be
utf-16le


Once you've found the right encoding, convert the file to unicode and re-save:

:set fenc=utf-8
:w converted_file