As a native Scandinavian, I understand most Scandinavian (except Finnish) without having spent more than fifty hours with various Scandinavians, and without having attempted to learn much. (It's mostly deciphering dialects, remapping certain words.) Having unwillingly learned German as a child, I can enjoy German television and navigate German cities as a confident, talkative tourist. Having learned fluent Esperanto, I can decipher a bunch of words in French and Italian, but can't follow conversation.
As for Chinese, 1.5 years in, I can form sentences like a shy 1.5-year-old: Anything above 3 characters is probably grammatically incorrect, or "you could say that... but a native speaker wouldn't." Different paradigm altogether. But a Chinese can pick up decent Japanese in less time. (https://www.quora.com/How-difficult-is-is-to-learn-Japanese-...)
Learning Ruby if you know Python is kind of learning another European language, if you already know one.
Learning Haskell or Prolog is kind of learning Chinese if you only know imperative languages.