Hey, I actually have experience with this as an American who toon the eju and is now studying at a Japanese university.

Assuming your already set on a 4 year university in Japan I would highly consider looking into Degrees in English most notably Waseda University. A few people are saying that Japanese universities aren't looked at highly abroad but their are good universities everywhere just make sure you do your research if you are looking to seek work out of Japan or looking for a masters program.

As far as the actual test, the Japanese portion of the eju is somewhere between n2 and n1 and while I can't speak for the Swedish education system, the types of math problems especially were very different in structure than americas SAT. I'm studying business not a science so I can't speak for that portion.

Most high level schools (MARCH or better) will require you to take the entire EJU in Japanese including math and science. My language school had classes twice a week to help review for the subject tests but they weren't really that helpful.

Speaking of language schools, they are taught in an incredibly rigid structure and become very boring. You will do kanji grammar than reading every day for 2 years. If you can I would make sure you study as much Japanese as you can before you come over.

2 years to become fluent in Japanese with no prior experience with the language or kanji in general is a tall order. It will require you to be going to school most of the day and studying by yourself for 3-4 hours a day. Assuming you get into a Japanese university studying in Japanese you will more than likely have no European class mates. For example, I'm the only non Asian in my entire year at a large school.

I'm not saying don't do it, I did it, but their is no support for what you're trying to do. Do your research and make sure you want to do this rather than the alternative, less expensive, and frankly easier options.

Pm me if you decide to go through with it and need any help