还是有区别的,second language是第二语言,foreign language是外语（非母语）.一个人的foreign language可以有好几种,second language只有一个
every language used by a foreign nation which is different from your native language can be called a foreign language.
however,the notion of a "second language" can be explained like this:
this is a language u also have a good command of.in offical or common accasions,u may use your first language as first prioriry usually,but when first language can't be used to communicate with each other,the second language is up to.