Earlier quoted context omitted.
I think your issue is just that your grammar was wrong. 是的(Shide) is the closest thing to yes in Mandarin, but it's as universal. Answering 是的 on the question 你会中文吗 is like answering "yes I am" on the question "do you speak English?". 可以 isn't correct either, unless they asked 你可以说中文吗?, which is more like "Can you switch to English?" And not "are you able to speak English?" if I'm not mistaken. Answering 我会 is perfec…
Almost related: Check out the various translations of the subtext of this manga (to Chinese.. etc) https://ja.wikipedia.org/wiki/%E3%82%8F%E3%81%9F%E3%81%97%E3...
Most titles read like the publisher just giving up and going for anything that doesn't sound crazy. Which is exactly opposite to the original title.