Taking a look at Minmatar 'culture' and some of the hints and bits we find in-game, there's many references to Obelisks, to Norse mythology, some african-style nomadic concepts and so on. Personally, I consider their culture while knocked out of the skies and re-developing after the Eve Gate thingymakablooey to have largely been a blend of Norse medieval style tribes, clans and such with the runes and all the fun bits that come with that. Toss in some germanic/anglosaxon Ye Olde stuff with obelisks and such, with a bit of african tribal culture and you have a very interesting blend of some of the most dangerous, yet culturally interesting parts of human history.
Now, as a faction, they seem to have managed to retain much of that while rising into their current status as a full-fledged faction. The inherent conflicts between the cultures in question seem to have realistically both bound them tighter while keeping them somewhat apart.
So as for writing styles, I would go ahead and say there's quite a bit of an oral tradition (common to tribal communities), artlike writing/scripture styles through runes and such along with powerful symbolism inherited from their ancestral culture. It would have to be up to each player to decide whether it would be a 'universal' Matari hodgepodge style of writing or some very distinct and separate styles between clans, tribes, bloodlines and so on.
Personally, I'm going with runic style lettering and widespread use of symbols that can have many meanings depending on context. And the same goes for many words, changing definitions depending on context, while retaining one core definition. Take the description of the Loki as an example.