This isn't so much a random thought as a random question, but it doesn't warrant it's own thread so I'm asking here.
For those of you who know such things, if I wanted to convey to a Japanese person that I don't speak/understand Japanese would I say Nihon-go wa wakarimasen or Nihon-go ga wakarimasen? The internet seems to be providing me with both versions. Also, should I stick Watashi wa... at the start or is that redundant? I've read somewhere native speakers often leave out that part of a sentence when it's obvious you're talking about yourself, the other person, your cat's mum etc etc.
Also, if you don't need watashi wa because that's not how fluent/native Japanese speakers talk, could it be advisable to include it so it's obvious I actually don't speak/understand Japanese, as telling saying it to someone in perfect, fluent Japanese might seem...weird?
A 2nd also - is it better to say I don't understand Japanese or I don't speak Japanese? Which one conveys the same meaning as saying I don't speak x language in English, or does it even matter?
Am I over thinking this? Maybe looking like a confused idiot will convey the same thing lol.