Planning to travel to Japan for year end and I definitely could use some new games there.

As far as I understand it, most (not all obviously) Switch games have English support, be it through a menu option or by following system language.

Does that really apply to "all" worldwide released games - i.e. BoTW, Xenoblade 2, etc - regardless if their so-called region and box cover are Japanese?

Is there any way I can notice it from the box?

I don't know about cartridge games, but I've downloaded games from the stores of other markets with no language issues.