I’m not sure I’d describe it as out of character.

Phonetically styled narrative from characters pops up in several Banks novels. I’d argue the The Barbarian’s Scottish dialect in The Bridge was a precursor to Bascule.

There are also smattering’s of fun phonetic speech in the first few Culture novels. Most memorably from Fwi-song the prophet of the Eaters cult.

I had the feeling with Feersum Endjinn Banks decided to go ‘all in’ on the fun phonetics.

In the early 90s I went to a Banks reading (possibly Crow Road or The State of The Art) in Sheffield and during the Q&A he talked with great animation and detail about his new as yet untitled novel, which a few years later turned out to be Feersum Endjinn.

Sorely miss him.