People with English as their second language make some very common mistakes while speaking or writing in English. 
The mistakes most of the times are grammar related, framing the questions in wrong manner or small preposition/articles mistakes. 
Some mistakes could be very embarrassing.English has a lot of commonly confused words. They either look alike, sound alike or, worst of all, look and sound alike but have completely different meanings. Other words look and sound different but are similar in meaning, and it’s hard to determine which is the correct one in a given context.