Hi Jun-san, Many thanks for your report and analyis!
I've tested the new upstream version 5.6.0, and it brings DroidSansFallbackFull.ttf, I guess this issue has been fixed, at least I'm getting mixed Japenese and English text in the UI, when I set LANG=ja_JP.UTF-8. But as I'm not speaking Japanese at all, this is just a guess… The bug will will be closed with the upload I'm currenty preparing. Please feel free to reopen the bug, if my guessing was wrong. -- Cheers, tobi
