Hi caothusieuhang,
Imo i think it would be pretty difficult to go straight into year 11 Japanese starting with no previous Japanese knowledge. However, you said you like anime and manga, do you watch it without subtitles? How much do you understand? I think being able to do this gives you a really good advantage/start. (I got a good score in Jap and still can't watch anime without subtitles). People who watch/read anime/manga tend to do better in Japanese than people who don't.
Are you in year 11 next year? I think you should try and get a copy of the year 10 textbook and work through it see how you do with it, and also please talk to the VCE Japanese teachers to see what they think, and they might be able to give/email you some extra work to help you catch up before yr11 starts.
The big difference from anime/manga and VCE Japanese is that VCE uses the formal ます/です form for pretty much all of it, so over these summer holidays you'll need to make sure you are comfortable with it.
I think the main factor in your decision is your motivation + self discipline. Are you willing to catch up on all yr 9/10 content by yourself on the summer holidays? Depending on your level it might be easy or hard for you.
Don't forget there are other options for learning languages; just because you don't do it in VCE doesn't mean you will never learn it (uni class, duolingo etc).
A pro for you learning Japanese in VCE is that you seem to really like it, which means you'll be more motivated to study and so it's easier to get a better score in a subject you enjoy. Also, for me Japanese was a very different subject from my others so it's nice to have that difference i thought.
Also, doing well in Japanese is a lot about how much effort you put in. There are students who started learning in yr 7 who get better scores than students who have one Japanese parent/have spoken it since they were young. To do well you need to do a lot of learning outside of class, so if you are really self motivated I think you'll be able to do it!
(also since not everything is about scores, you could take it because you enjoy it even if you might not get a good score (so long as you feel comfortable that it's not going to cause extra stress for you by being a bit behind) --> look over year 10 (+ VCE) textbooks to judge this). I think it is likely you'll feel a bit overwhelmed when you first join the Japanese class at the beginning but you'll probably find you have certain parts you are stronger than others in, and others you'll have to relearn/practice at home. You'll need to put in extra time and effort to catch up, but it is possible to be done I think.
Good luck with whichever you choose!!
