fsc fails on files with Japanese characters in the file name, although scalac works fine. The output hints at problems with handling the argument and also the output encoding (although the latter may be because UTF-8 has to be forced on Mac Java, which does not set the output locale information correctly).

fsc 空気清浄機.scala
error: source file '/tmp/?????.scala' could not be found
one error found

scalac 空気清浄機.scala

• no errors, result is 空気清浄機..class as expected.