I am currently in the early stages of mapping out a conlang for a race of boar-people. I was stumped trying to think of what limitations, if any, having pronounced lower tusks would have on the development of their language. These creatures do have snouts, but this question more than handles my needs on that front.
I'm really more curious about the effects tusks would have on their speech from that point on or in general.
They will have the ability to develop an oral language much like ours, but the details will depend a lot on the precise anatomy of the mouth, especially the lips.
Unless they cannot close their mouths completely due to their tusks (which is highly unlikely), I think they will have no trouble producing bilabial stops (/p/, /b/ and nasal /m/). Even if the lips cannot seal the mouth, if a reasonable length is closed, the "popping" effect of a bilabial stop can be achieved. It may be that these sounds will not be distinctive enough, though.
The same goes for labiodental fricatives /f/ and /v/, which don't need full closure of the lips. Indeed the tusks could conceivably function as a secondary fricative articulation.
They might run into trouble pronouncing rounded vowels (such as /o/, /u/ and the front rounded vowels of French and German) and the consonant /w/, if the lips are not flexible enough or the tusks are too close to each other.
As for new sounds, I'm picturing maybe a bilateral fricative or approximant made by letting air out the corners of the mouth, left and right of the tusks, while the lips are pinched in the middle. You can do this yourself if you pinch your lips right behind your nose using your index finger and thumb and forcefully blow some air.
Well sounds that are generated by putting your lips togheter like 'm' , 'b' or 'p' would certainly be much harder to make due to certain parts of the upper and lower lips not being able to join especially the labiodental fricatives like 'v' or 'f' .
But other sounds would probably be developped, based on the flow of air around the tusks, if their entire culture developped with this physical particularity, they'd probably still have pretty effective speech, some of it would just sound much more different. Another thing I can think of is, due to the lips curling slightly inwards and the tiny gaps between the lips around the tusks, their voice might sound slightly cavernous.
