Hi - my first post here on Core77.
I’m an IDer working in Japan, and am fluent in Japanese and speak intermediate level Chinese.
If you’re aiming for a career in industrial design and are hoping that the languages might help you get there, then Chinese will give you the best range of options. If you really must choose between Japanese and Korean (as per your original question) then I’d choose Japanese. Remember though that if you want a job as an industrial designer in a Japanese firm, you will need to have a very high level of Japanese ability for the firms here to take you seriously over other Japanese graduates. The standard here is very high, and a lot of Japanese ID graduates are very very talented (I should know… I work with them!)
Hope this helps. Good luck for the future.