Yep, that's mine :)
Just to be absolutely sure: you understand that the LanguagePrefix module is an extension on the Translatable module. So you I assume you tested this on a SilverStripe install with Translatable, but without LanguagePrefix?
If that works as well, then the issue is indeed with LanguagePrefix, and I'll need your help with figuring it out, because i don't know any non-latin languages :(