If I had a time machine, I might well go back and become a mediaeval Sinologist rather than a mediaeval Celticist, not least because Chinese is a lot easier to learn than Welsh. (My Welsh tutor refused to believe this; my various Chinese tutors find it hilarious.)
My Chinese is very rusty these days: I haven't been able to afford lessons for several years and I'm forgetting stuff. I try to keep it going by watching tv shows from China and Taiwan.