Rin knows how to speak the human language, but does so slowly, hence all of the pauses when he speaks a sentence.
Was that established at some point (that the dog speaks multiple languages)? Because in Chap 44, it's established that during the first conversation, when Rin's also doing the overly-punctuated speech, nobody actually knows what he's saying aside from the MC because it's not speaking human language. So it's not like he speaks fluently in dog language, to show some kind of difference between using dog+human languages. It seems to me like the dog only speaks one language, even if it can understand beast+human.
I assumed the punctuation was just because it's not actually a dog, so even if it's using a canine language (as implied by Khema barking at it) it's not good at it either. There's also the bit about Meat failing to negotiate with him because she doesn't understand most of what it's saying (because she's not 100% fluent in beast language), which wouldn't make much sense if he was speaking human.