Comment by nxor
What do I mean? Where to start. Interact with some people from the region and you will find out. As most learners of German know, the hard part of German isn't der die das, it's the exclusive culture. I have C1 in German and have been told "You sound unnatural like a Turk" (I am not a Turk) and "Children sound more natural than you" (of course - they are native speakers). You can get every case, every article, and every syllable correct and they will still find a way to laugh at you. Ask for help in Germany and you will be ignored. Or better yet, "I don't want to help you." Then they wonder why people fail to learn their language. Frankly I wish I could unlearn the language.
> You can get every case, every article, and every syllable correct
For articles, natives say sentences with wrong articles in them too. Seldomly because they don't know it (still happens), but because they change what they want to say mid-sentence. Cases are always a fight between the pendants and people who don't care.
Plain incorrect grammar will of course be noticeable, but grammar isn't everything.