To learn a foreign language is difficult.

There are many difficulties in learning a new language. First of all, culture of each country is different in many ways. Each countries organize ideas differently. There are many differences in ways of life, their thinking method, their talking manner, their making relationship, etc. Second, language is composite of reading, writing and speaking. For example, we don’t learn a foreign language completely if we study reading, writing, speaking separately. In addition, we always use mother tongue, there are a few chances to learn foreign language. We haven't any chances talk to foreign language.
These reasons explain to us why learning a new language is difficult.