I wrote two little macros, uchr$ and uclen:
mov esi, uchr$("No, it is plain English - SORRY!", 13, 10)
invoke MessageBoxW, NULL, esi, uchr$("The text in esi might be Chinese:"), MB_OK
invoke MessageBoxA, NULL, str$(uclen(esi)), chr$("The text length is (in bytes):"), MB_OK
Full code in this post (http://www.masm32.com/board/index.php?topic=9936.msg72979#msg72979).