What's the meaning of the spell's name that Wendy uses to cure Natsu's vehicle-sickness?
This is probably just a random word created by the mangaka for the spell's name. It's probably just a coincidence that Troia meant whore in Italian translation. After all, it's a healing magic so it won't make sense that the mangaka chose that kind of word intentionally if knew that meaning in Italian translation. You can find Troia's full description here.