Well, most players don't care. However in games with enough population you are likely to have role-playing guilds which will go to some trouble to role-play and yes, that involves the language used in chat (on the third tentacle there is always an OOC (out of character) chat channel where you can speak normally).

Gender-wise, everyone is assumed to be a guy -- unless (a) you explicitly declare yourself a girl; (b) you are on voice comms and your voice is clearly that of a girl; (c) you're in guild chat where people know that you're a girl.

It's hard to get players to use specific speech patterns, and harder to teach them to get it right. I've worked on a game which tried to get players to use pseudo-Elizabethan prose (in a particularly ham-handed way, granted), but in practice what happened was the people who didn't care just used natural speech, and the people that did used whatever butchered old-timey dialect they thought would be appropriate for their character. Most people didn't care.