Coin names and slang: adding character to games with ease

Most custom settings seem to consist solely of a generic map and a custom pantheon, which doesn't do much in my opinion apart from boring the players while the GM rambles on about how Qwertix defeated Zyxx and so on, which does nothing for the players or, worse, proscribes a clerical domain or two. So how does one spice up a custom game?
It is often said that the theme is key, however this may result in a gargantuan job, so minor details are easier to pull off.