Depending on how well you want to master the language, I believe it can be somewhat difficult, but can be easily mastered as far as being conversational. From the outside looking in, English has many homophone words, and that can be trying to those who are looking to learn the language. Also there are many phrasal verbs, and those can take time to master. English grammar can be tricky, as there are numerous ways to write the same sentence or phrase. All in all, with practice, the way English is compared to other languages, is similar in structure, and can be picked up quickly, with enough practice.