[hgsgm]

There is no such thing as a grammar mistake, only a grammar inconsistency. Intelligent people use grammar consistently up to the moment where that consistency impedes clear communication. A grammar "mistake" is a foreign dialect.

Unintelligent people babble wisps of ideas and leave it to the listener to make sense of them.

[mc32]

I disagree. When I took foreign language classes I wanted to apply the prescribed/common grammar rules, but I mistakenly used them incorrectly. I wanted to do apply the rules as a native would, but I got it wrong despite my desire to get it right. Therefore I classify that as a mis-take.

[liquidk]

It depends. English is a lot more tolerant of inconsistencies than latin based languages, and the grammar rules are more disperse. Typically in latin based languages the rules are stricter, and it is less socially acceptable to violate them. English is surprisingly tolerant both in the rules and the social acceptance of not following them.

[mc32]

It's a good observation. In my experience, often speakers of non-English will suggest that we switch to English because they feel uncomfortable with my mistakes in their language, rather then put up with my attempt at speaking their language. English speakers don't typically do this even when they are versed in a second language.