【Language Detection】 Wrong language detection and Decreasing detection quality when specifying language

[sayeka0119]

Background: I bought a DVD and got its video.
Question:
1 Although I have cut the long video into small ones, whisper cannot correctly detect its language. It always detects the language as English or Chinese, but actually the video is Japanese.
2 When I use --language , the transcription quality is much worse than the one without --language
My goal:
I want to make whisper correctly detect the video with normal quality and accuracy.