For me the challenges of language learning is my mind set.

    I had italki classes more than 100 classes so far but my English skill improve a little bit especially  speaking skill because I'm a lazy student I don't like homework Iand I'm a thoughtful person example If I have to speak or communicate with other in english I always worried about the sentences that I speak out are polite or not? Is it  weirded ? or sound strange so the easy way for me just avoid to speak english with strangers and practice english only on classes.

For me the most challenging thing about language learning is my mindset. So far, I had taken more than 100 classes on italki, but my English skills only improve a little bit especially my speaking skills. 
Why only a little?  It's because I'm a lazy student and I don't like (doing) homework.
Moreover, I worry too much about the words or sentences I use. 
For example, if I have to speak or communicate with others in English I always worry about my sentences whether they are polite or not?
Is it weird? Or does it  sound strange? So, the easiest way for me is to avoid speaking in English with strangers and to practice speaking in English only in classes.