I can only really speak about Japanese, but tbh this goes out to all of your threads:
You will be fighting a losing battle.
It doesn't matter how motivated you are, learning another language is /hard/. Particularly for Korean and Japanese, you'll need to learn entirely new alphabets along with words, grammar patterns, cultural classes, etc. If your only incentive is that you want to learn a new language, do it in your own time - with the popularity that's come with apps like duolingo, it's honestly not that hard to start learning a language all by yourself without formal education. Plus, there are plenty of classes for adults where you can get actual experience - there's even a bunch of groups that will literally just meet up in a pub, and the whole point is to just sit there making casual conversation in a different language. Seriously, learning a language has so many less barriers than it used to - you don't have to get a formal education anymore for people to think you're a fluent speaker.
If your aim is to get high scaling subjects, this is not the way to do it. I did this in year 12 purely because I had already done year 11 Jap, and figured I should do year 12 for that extra scaling boost. I would honestly have been better off taking another subject - I did so poorly in Japanese as a result, that my score didn't enter my top 4 /even after scaling/.
If this is because you like languages and want to do them because you'll feel you'll be more motivated, figure out what it is about languages that you like, and try to find subjects that can still give you that thrill. Maybe it's because you love learning about culture, so it may be worth taking history and learning what culture was like all those years ago. Maybe it's because you like analysing how language comes together and forms, and so you might want to consider taking English Language. I know it can be very easy to sit in a pouty little hole and say, "no, I like languages because I like learning new languages", but if you do it this way you will only hurt your ATAR.
Unless of course you've decided on a pathway that won't require an ATAR - in which case, do whatever you want. You can't fail VCE as long as you do all the work, even if you get 0 in all your assessments.