dnd 5e – Rules for learning new skills in D&D

Are there any rlues for learning new skills and abilities?

I wonder if a character can teach his skills other party members.

Let me present some examples:

Let’s say I am playing as wizard and I want to play a bladesinger with a high variety of weapons. The problem is bladesinger gets proficiency in only one melee weapon(https://www.dndbeyond.com/classes/wizard#Bladesinging) So I want my fellow warrior to tech me martial weapons proficiency.

Or, for some reason, I want my friend ranger to teach me stealth.

Let’s say I want to teach my comrade some basic spells. I am a wizard so, as lore states, I learned them, probably from others wizards. It could means I can teach magic.

Or, I simply want to learn a language from my party.

End of examples 🙂

So, what are the rules for that? Any attributes prerequisites?
I am playing in D&D 5e, so I am asking about the rules in this system.

Yes, I know that in this case the concept of classes becomes meaningless, but let’s ignore that 😛