Myself I am not aware of a point like that. Accents that are hard to understand (impossible is always debatable, but if you can read it aloud and get the general idea, it isn't a problem) can make some interesting RP trying to understand what they are saying, as it is rephrased a couple times perhaps... or a misperception, which can make a relationship between a couple characters suffer.

Butchering of the language can be taken IC... think about it, if you have ever tried to speak a second language, there is expected to be some confusion... if it is a written speech, and I speak English as a primary language, and perhaps I try to write something in, say, German, for example, it can be expected to be problematic in this situation. It is a difficulty for that character to communicate if they only know a little bit of the language.

About the gaps in speech, sometimes that is just a way someone thinks. Their mouths go much slower than their mind, leaving the other people to guess... or maybe they created their own slang that is only well known to those that know the character personally...

In the end, I think if speech is taken as something IC then it doesn't really distract from Roleplay.