"누구든지 한국어를 배워도 돼요."
Translation:Anyone may learn Korean.
Technically, in English, "Can" and "May" have 2 different implications.
"May i go to the bathroom?" and "Can i go to the bathroom?" while meaning roughly the same thing are not exactly the same and in certain circumstances are not interchangeable.
E.G "The Policeman may come round the corner" and "The Policeman can come round the corner"
The former indicating a degree of likelihood of the action occurring as opposed to the latter statement indicating that the action is just possible.
Does the same principle follow in Korean?
While in English that may (notice my use of the word may ;) ) be true concerning the differentiation of can and may. If you penalize the learners on the simple fact of their misuse of the word "can" it will make the task of learning much more strenuous.
While I can agree to your point you have to realize the English language and the Korean language run by different rules while they both have words that correspond to each other in meaning at the end of the day they don't exactly mean the same thing entirely. Since the use of can and may are so closely used with each other it's probably better to leave both as options.
Also, keep in mind while one word can have multiple meanings in English that same word in Korean could have just one, or even more than the English equivalent, or be used in an entirely different way.
How I understand these pronouns •••
▪누구든지 = anyone (any person) who/whom / Whoever; whomever. e.g.
헌신적인 사람이라면 누구든지 한국어를 배워도 돼요. Anyone (who is) dedicated can learn Korean. / Whoever is dedicated can learn Korean.
나는 내가 원하는 누구든지와도 함께 어울리겠어. I will hang out with anyone whom/whomever I want.
▪누군가 = 'Someone, anyone'
누군가를 만났습니까? could mean "Did you meet anyone?" [Expecting a yes/no answer]/
"Have you met someone?" [Expecting some story to a foreknown 'yes' answer]
내가 없는 동안 누군가가 전화를 했니? Did anyone call while I was out?
누군가가 전화를 걸었지만 메시지를 남기지 않았습니다. Someone called but didn't leave a message.
Both are okay as long as you know "can" is also used to express ability and possibility ( Vㄹ/을 수 있다 )
-도 되다 is used to express (both for asking and granting) permission politely, not making one sound patronising.
도 돼요 = may [ by extension: could; can; is all right (okay) to ] ...