@Sewil:
There's plenty of ways to translate the word to an equally mystical/magical appeal by just localizing it to the point where it doesn't have the same literal meaning, but where it instead gives the same reaction to that of a Japanese.
For example, here in Sweden, the word for Haki has no real connection to ambition/spiritual power or whatever. It's a word that implies the person in question gives the impression of a certain power/authority/rank/value, Pondus.
In my opinion that's a great translation, and it fits with Haki's abilities, while Ambition seems like a weaker word for it.
"Pondus" describes the perceived weight/influence the bearer holds in society/group/organization, but it does not describe the bearers level of ambition/willpower etc. A person born into power and with low ambition/willpower will have less chance of fulfilling any dreams of their own. They run the risc of being manipulated instead.
A person grinds himself to a position of power, and the higher he comes in terms of "pondus" the easier it will be to fulfill the dreams of his ambition by people obeying his orders/actions.
So the swedish word for HAKI does not match the fact that op-persons HAKI strength gets stronger through personal training, not by how people percieve you.
Perhaps you get it I am swedish too :)