Hi, it's great to hear about your interest in SOAS and your passion for Chinese ethnomusicology!
I completely understand your concerns, but I wouldn't worry about being seen as "weird" at all. I'm currently studying Arabic at SOAS, and a few students in my cohort come from Arab backgrounds, but I've never once thought of that as strange.
As for the language aspect, SOAS is really good at accommodating students with different proficiency levels. They can assess your language ability before you start and place you in the appropriate class. For students who exceed the highest language modules, there are modules that go beyond focusing on language learning to examining literature and film or even writing a dissertation in the target language. So, hopefully, you'll still find ways to be academically challenged.
If language modules aren't your main interest, the East Asian Studies course offers a wide range of non-language modules too. SOAS has some unique options, like 'Myths, Legends, and Folkways of East Asia' and 'The Confucian World through Women's Eyes', as well as modules exploring politics, history, and culture, which could complement your interest in Chinese ethnomusicology.
If you can, I strongly recommend attending one of SOAS's Open Days. It's a great opportunity to chat with staff and students from the department about your goals and concerns. They also offer taster sessions to get a feel for the course and the teaching style. If this is something you'd be interested in, you can book a place here:
https://www.soas.ac.uk/about/event/undergraduate-open-day-0Good luck with your decision, and feel free to give me a shout if you have any other questions!
-Szara