I do not know the Wireshark code, so I am not submitting a patch. This, however, should work because JSON supports UTF-8 (see again [1]).
What do you mean by "I do not know the Wireshark code"? What did you patch? Do you mean you don't know the submission procedure instead? If that's the point, just file a bug report on bugzilla, with your test case, and the above patch if you care, and wait for someone to take care of it :). Posting the bug report here will speed up the process if someone is interested in patching the code for your case.
Hope it helps.
Dario.