also i wanna say as well, luca's speech impediment is very likely from his dental/mouth injury that he has (the reason why he has his tooth sticking out like that, that is highly likely to be caused by an injury)

Having misaligned teeth and problems with your mouth affects your speech a lot, people don't realize but having like, a misaligned jar or other dental issues affects the way you form words, since you use all sorts of parts of your mouth to speak

I don't have all of Luca's replies on hand, but it seems he struggles with forming "w" and "b" sounds with his mouth

to form a "w" and a "b", you have to purse your lips together, so trying to enunciate these sounds is probably really painful to do, hence why he slurs them

SORRY IF MY EXPLANATION WASN'T CLEARER here's diagrams of the mouth positions of forming "b" and "w" sounds!