No language is impossible to learn. Some languages are easier to learn and others aren't so easy. So I have a couple of questions for you here.
What do you think is the hardest language for you to learn? What would be the hardest challenge for you?
Do you consider your native language hard to learn? What would be the hardest part about your native tongue?
I think the hardest language to learn for me would be Chinese, Japanese or Arabic. I think the different alphabet and not hearing those languages around everyday would make it too hard for me to learn.
And yes, I do consider my native tongue hard to learn. Estonian has 14 cases, which makes it hard to learn for people whose native tongue has only few cases. I've also read a few articles by foreign people who are studying Estonian, saying that native speakers wont let them even practice the language and tend to speak English with them.