Hi,
you can specify the encoding of the source files as well as the encoding
of the html report e.g. with our Ant tasks:
http://www.jacoco.org/jacoco/trunk/doc/ant.html
I don't think I fully understand your question, but UTF-8 as for the
html output should work for japanese characters. Maybe there is an issue
with the source file encoding on the input side?
Regards,
-marc