Firstly: sending multi-byte characters as part of a filename to Audiosurf still seems to crash it. Notably Japanese ones.
I'm not sure where things are going wrong because 7-bit original ASCII character (1 byte under UTF-8) work fine as do 16-bit, 2-byte UTF-8 characters. But it seems 3 (and presumably 4 as well) byte characters such as Japanese kana don't work and cause Audiosurf to crash as before.
Secondly: quickstartregisterwindow appears to be broken. The normal registerwindow does work however.