There is another reason: People understand you, interrupting with corrections hurts the conversation. I often ask for corrections but nobody ever does it. When I'm unsure how to say something I sometimes ask to get some feedback. Sometimes I only understand 70% of what a person is saying (mostly due to dialects), I rarely need to ask them to repeat it because the brain is capable of piecing it together.
Another problem is that unlearning something you always did wrong is extremely hard. You need to get it right from the beginning.
That's the beauty of language school, they point out your mistakes early and you can learn from the mistakes of other students in your group. If you take the time and take real classes, you'll have that tight feedback loop you need.
In my experience, people are helpful. Sometimes, in Norway, it means folks speak English with me. Not so much now, but once I struggle, out comes English :D But it also means that folks will let me know the right words for things or help with sounds. But at other times, folks will let things slide as long as I can be understood.
I can't recommend actual language classes enough. I was in Norwegian classes for two years - immersive classes for adults, taught by native speakers, about 15 hours a week in class. All in Norwegian, from the beginning. It was so wonderful getting real-time corrections and as an added bonus, a lot of culture/civics was worked into the lessons as well, in no small part because vocabulary centered around fairly practical subjects. If I ever need to learn another language, I hope I can have something similar.
I took them in Norway: Part of my immigration required that I take Norwegian classes. They were free for me, and were the ones offered through the kommune (here in trondheim) though I think they cost around 9000kr per 6 weeks. The class was mostly filled with folks with family immigration and folks fleeing bad situations in other countries (at the time, a lot of folks from Syria and Eritrea).
We used the books "På vei" and "Stein på stein" the first year. The second year I took "helsenorsk" and we used different materials, but for the general learning we mostly used "Norsk gramatikk", which, as you guess, concentrates on about a B1-B2 level of grammar. The first year books come with optional audio, which we used in class, and both have workbooks. I used one other book, but I don't remember the name. If he's determined, he can work through the books but understanding folks is going to be difficult (some dialects are still difficult for me).
NTNU offers a free online beginning course: They also offer classes, but those are filled with current students first.
I'll add that the level of Norwegian he'll need depends on what he'll be doing here: If he happens to be getting married and is from outside the EU/Schengen area, he'll probably have classes. If he goes to university, he'll need Norwegian for a bachelor degree, but a lot of classes above that are in English. Work really depends on the field, but even in fields with lots of English in the professional realm, knowing some norwegian will help lots.
Another problem is that unlearning something you always did wrong is extremely hard. You need to get it right from the beginning.
That's the beauty of language school, they point out your mistakes early and you can learn from the mistakes of other students in your group. If you take the time and take real classes, you'll have that tight feedback loop you need.