grammar

There are many people in the world studying English, so English people are used to learners' non-standard accents, their grammatical errors and so on.

This sentence is grammatically correct.

Interlingua is an international auxiliary language developed between 1937 and 1951 by the IALA (International Auxiliary Language Association). Its vocabulary and grammar is chiefly derived from five control languages: English, Spanish, Portuguese, French, and Italian.

Grammar is a very complex thing.

The grammar of Esperanto is very simple.