I stumbled recently into reading about the Chinook Jargon, a pidgin language formerly widely used for trade in the Pacific Northwest, which drew vocabulary from native Chinook and Nootka languages as well as English and Canadian French. Nominally it has/had about 700 words.
An 1889 Chinook Jargon dictionary from Project Gutenberg is an interesting skim. Lots of concrete nouns for animals (including pests like lice vs fleas). Body parts. Colors. Social relations (like one's brother). Kinds of people (I particularly love that "Boston" is a noun meaning "An American"). Weather. Objects like combs and guns and money. Verbs like want, go, give, come, dance, tell, injure, and lie. Numbers. Time, days and weeks and seasons.
Lots and lots of overloaded meanings. Tum-tum is both the literal heart and the figurative will or opinion. Skookum is both strength and ghosts.
Lots of meanings from assembling other words. Hyas is high or big. Puss-puss is cat. Hyas puss-puss is a panther. Halo is none or without; halo wind is without breath, eg dead. East is comes-sun, west is sits-sun. Skunk is stink-tail; rattlesnake is rattle-tail.
The connection to gaming is probably obvious. If Common is a trade pidgin, your players probably shouldn't be having philosophical conversations with captured goblins in it. I'm not saying you should write a list of 700 allowed words that your players can use when speaking Common, but... I'm not saying you shouldn't do that either. A limited vocabulary creating a need for figurative language could create lots of room for amusing miscommunications.
It could be pretty funny, and not entirely unprecedented - I seem to recall a caveman RPG that restricted the number of words that players had access to (Og, perhaps?).
(Obviously, the reasonable thing to do would be to stop players when they try to use Common for abstract conversations, but where would be the fun in that?)
