I've occasionally thought about what victory conditions would promote roleplaying, but I haven't come up with a good answer yet.
For in-character diplomacy, I like to write in a style that fits the background I've imagined for the race.
When I'm playing my Rrurrr, I often speak of Honor, and mention the Ancestors a lot.
example...my mi-go alwayz whizperr with no capital letterrz...few conjunczionz...the only punctuazion they uze iz the ellipziz...
[The Mi-Go also "roll" the letter 'r' and replace most 's' sounds with 'z'.

]