Linguist? No...knowing another language doesn't make you a Linguist. Linguistics is the study of how human languages are constructed, not the study of learning to speak additional languages.
Translators need to be completely fluent in both languages. Learning a language in a purely academic setting can get you to a conversational level, but not 100% fluency. You need real world practice with a language to know the nuances, slang, etc. of each language.
If you want to learn Japanese, I suggest you double major in Japanese and Business. That would give you an opportunity to be hired with a company that deals with Japanese contacts/clients.
A major is the subject of your degree.
ex. Bachelor of Arts degree in "________"
The blank is the major. In your case, it would be Japanese.
A minor is just an optional way to take a handful of courses in another area. You don't get a special degree or certificate for it. People do minors either to complement their major with some additional knowledge, or just to pursue a personal interest.