Vocabulary difference is a huge issue though. Korean and Japanese grammar is very different from Chinese, but the shared vocabulary (of Chinese origin) makes it

Vocabulary difference is a huge issue though. Korean and Japanese grammar is very different from Chinese, but the shared vocabulary (of Chinese origin) makes it easier to learn one of them if you already speak another one. Also incentives and resources in a target language are very important. Assuming you don't know a Slavic language (I don't), take a look Interslavic. I recognize zero words in the example texts. That might make sense to someone who knows one, but it's going to be an uphill battle for me. Honestly I'd rather invest time in something like Russian or Polish because it gives me access to a lot more native speakers, media and literature.