I have frequently worked with ESL students who experience difficulties acquiring a new language because they struggle with language impairment. Often people ask how a language disorder can be distinguished from simple normal language acquisition. It’s not always a simple answer, but one place to start is with the acquisition of the first language. If someone has problems acquiring their primary language, then it is highly likely that they will also have difficulty acquiring their second language. However, someone may not show signs of a learning difference in their primary language and still have a learning difference that presents itself only when they attempt to learn a second language. Here is a link for more in depth information on this subject.