I participated in a couple of pbems, and the Messages sent ingame are far more often in-character than not.
I personally tend to adapt a language I find suitable for the nation I play - Marignon with all its fiery passion for the unbelievers, R'lyeh cunning and subtle and shifty, Ermor laced with dark poetry coming from the Mouth Of Doom... And I only drop it when the replies don't come likewise. So far, though, the results are pretty satisfactory, roleplaying wise. I don't think I'll grow out of it.
