Learning a new language requires a lot of effort and time. There are no shortcuts, you have to put your time and your heart into it. The most common challenge language learners face is to keep motivation up for enough time. Many learners start off very enthusiastic, but this enthusiasm fades away after weeks or months. Aside from the emotional, psychological aspect described above, there are other challenges that people face in the path to mastering a new language. Wrapping your head around unfamiliar grammar rules is often seen as a dreadful task. This one I can attest myself, for my native language doesn't have the concept of present perfect and simple past, so I have a hard time identifying when to use each in English. The last challenge I want to talk about is related to availability of learning resources. This isn't a challenge for those who learn popular languages, such as English, French, and German. Those who learn more "obscure" languages, however, may struggle to find high quality resources. Also, if we see native speakers as resources, then languages such as Swedish and Dutch impose a very peculiar challenge: most native speakers are fluent in English, so they will default to English as soon as they catch your first grammatical mistake. This impose a surprisingly difficult challenge for high intermediate speakers who want to become fully fluent. The three main challenges in language learning, in my opinion, are: lack of motivation, getting used to alien grammar, and finding good learning resources. There are far more challenges, but those are the ones I see the most in language learning community.