> There is no reason to discuss legal obligations because that part is covered by licenses.

Correct, I think we agree on that.

> The entire discussion is at the level of social expectations.

No, this statement:

> No, there is no obligation. But there’s a thing called courtesy.

Is actually “No, there is no legal obligation. But there’s a thing called courtesy.“ And here the contradiction falls away and the discussion turns to whether there is a social expectation to be courteous. On that point my (and the above commenter, I suspect) would say that yes, of course there is an expectation of social courtesy. There’s one in every other setting too, so why not here?

You are not "gingerlime" who said that, I understand the original as "moral/social obligation" and not "legal obligation" but you seem to be putting the word "legal" on the users' mouth by saying what they "actually" mean?

As a Spaniard living in Japan, what social rules should I use to apply my social courtesy on Github?

I am gingerlime. I simply meant obligation as MUST and social norms / courtesy as SHOULD. So I guess technically you’re correct that it’s not a legal obligation, but I think the GP’s point is valid.