"Do we really need to master a programming language to make games or programs? Like, do we need to know 80% of that language?"
"How many months or years would it take to master or be familiarized with the language?"
As advertised, generally you require no coding skills to create a game with construct 2.
The amount of time required differs per person, generally your background is of most influence.
If you know other languages, it would just be learning the correct syntax and approaches, seeing as how most code all does the same, just written a bit different.
If you are totally unfamiliar with writing code, then it will mostly depend on how you intend to learn it.
If you plan on learning lots of little tutorials and try to snatch just pieces you need; then you will likely spent a lot more time learning that language then if you were to take a course for an x amount of time, which would cover all the basics.
I learned most by the former, but in hindsight, would advise the latter.
I've been writing codes since GW basic and know how to make programs in roughly 10 languages ... surprisingly, apart from the whole object orientated approach, lots is still named and applied the same as it was 20 years ago.