Hi locchi, thank you for your interest in VocalSlice. The program does have the ability to transcribe and slice Japanese! However I noticed when testing today that there were some issues displaying Japanese and other international characters in the search box and transcription editor.
I will release a fix for this today (VocalSlice v0.1.9) which will fully support rendering of Japanese characters. I would really appreciate you trying it out and providing feedback.
VocalSlice should be great for slicing phrases/sentences out of larger recordings, but may struggle with precision if you try slicing letters/syllables within words. You can try changing your selections and attack/release times in settings to add buffering around what you are trying to slice if you have issues with accuracy.