Green’s Dictionary of Slang

(US) an English translation of a text in a foreign language.

1856		B.H. Hall College Words (rev. edn) 255: A translation. Hobbies are used by some students in translating Latin, Greek, and other languages.
1940		M. Marples Public School Slang 52: One who used cribs was said to ride hobbies, that is, apparently, to use an artificial means of reaching his destination.