[eukgoekoko]

> It is not that different from German in this matter.

I've met several Germans who spoke Russian fluently, none of them has really mastered the instrumental case, not even a friend of mine who worked at the German embassy in Moscow. Although you might say it's a minor grammar difference, this particular grammar case seems hard to grasp for people who are not accustomed to it through their native language.

Also, from my personal experience, quite a few Germans who learnt Russian had a real struggle understanding the concept of perfective/imperfective aspect.

[adrian_b]

These kinds of grammatical difficulties are typical for people who are learning only their second language after their native language.

After learning 3 or more languages that are not closely related, one is usually exposed to most grammatical features that can be encountered in the majority of the languages, so usually grammar no longer poses any challenges, but only memorizing the unfamiliar words and pronouncing sounds that do not exist in the native language.

[forinti]

I find the concept of perfective/imperfective verbs quite easy to grasp.

Remembering all the verb couples, that's what takes some effort.