you should probably be asking yourself why you're changing your major to Japanese? What kind of jobs will you find with this as a major? why were you minoring in it in the first place?
The only jobs you'll find in "design" is probably going to be sales jobs. Mostly furniture sales and if its retail, its weekends, nights long hours and holidays.
You should probably assess what it is you really want to do and go for it. Even if you finish a degree in Interior Design, you're not always guaranteed a job in the field. Work hard in school and your portfolio. That will get you your first interview.. and network network network!!!!