What is the link between the spoken incantation and the casting of a spell in Harry Potter?

Question

In Harry Potter, you have to pronounce (or think) a string of sounds to cast a spell.

For example:

Stupefy!

That always seemed very strange to me. So I would like to know:

• Are the words really necessary, or is the intention enough?
• If so, why are nearly all incantations in broken Latin?
• Do e.g. Japanese wizards have to use Latin incantations too?
• We saw with sectumsempra that a spell has its standard effect even when you don't know what it is, proving that the incantation does contain information. Does that mean that some words are magical? Were they always like that, did they evolve naturally, or was the word enchanted at the creation of the spell?

To sum up: what is the link between an incantation and a spell?

Answer 1

The link between an incantation and a spell is the same as between a name and the person. When you know a person, you don't need the name. Your intention is enough. But if unknown, the name plays a crucial role in identification

Similarly when you know the spell well enough you can perform it without the incantation. But if you are not familiar much then you need the incantation to hold the spell and release it.

Answer 2

Since (most) spells are casted using a wand, incantations may be used as a communication between a wizard and the wand.

Hermione had a lot more luck casting spells because she pronounced them precisely, this might've meant that it has been really easy for her wand to understand what kind of spell has to be casted.

In later years, as wizard develops a deeper connection with a wand, while rapidly using it he might develop certain connection or a way to telepathically order the wand what kind of spell has to be launched.

This theory might also explain why incorrect pronunciation, from some students caused them to cast spells that went differently then expected.

I guess that would mean that wands understand Latin so good is because they are made using specific traditions, standard model if you will, that would be implemented to make teaching of the spells easier for the teachers, although this does not rule out the possibility of Japanese-speaking wands