Yes.
Last year I did 3/4 Chinese in Year 11 and this year I'm doing 3/4 German. I don't Japanese (so I can't comment on the similarities between the two languages), but like Leezy said I'd strongly recommend doing one in Year 11 so it does lighten the workload. Many Canto students at my school/friends did Chinese 3/4 in Year 10/11.
Having already done a language, I already kinda know what to expect this year because outcomes are pretty similar, and you also know what kinds of text types you need to know, what questions will be in the general conversation etc
But yeah, I would suggest doing two languages because:
- scaling (OK, I know they keep saying 'don't pick subjects because of scaling' but languages do scale quite a bit, even if you don't get a super high raw score you will still get a decent scaled score - and yes it does require effort but it all works out in the end
- benefits of learning languages (I think you'd know this already, but idk personally I find it interesting to learn about other languages and cultures)
especially cos you've been doing Jap for so long, I wouldn't recommend dropping it.
But if you're not confident with Chinese, then don't do it because Chinese is super competitive as most people (even SL kids) are all super fluent in Chinese whereas most Jap students aren't background speakers. Half the time I keep thinking 'why am I even doing Chinese?' I'm interested in learning Chinese but I didn't feel my abilities were suited to doing VCE, but I still did it anyway and got a scaled score in the 40s so yeah.
Good luck