An interesting thing I've noticed about language learning is that it is different from most skills in that the vast majority of its practitioners are basically expert level. Learning a new language is uncommon enough that I rarely met other people who had spent the same amount of time learning the same language as me. So you end up judging yourself by an internal sense of progress, by the things you can and can't do. This is sort of like if you were learning to play the piano and everyone else but a few dabblers were playing at or near the level of Mozart. Also interesting is that language learners are always a master of at least one other language, so you inevitably compare yourself in that way also. It can really skew your expectations.

Also a lot of times in language learning is sort of all our nothing. Comprehension drops very fast or each additional thing you don't understand in a sentence. So progress can feel very slow and then suddenly you have a big jump in understanding.