How we feel and the way we express our feelings when we're in love, in a certain extent, depend on the cultural environment the lover has been raised in. Culture and language are always closely interconnected. So, the best language for a lover to explain their feelings, I think, is the language of the country/culture the lover is closely related to. If, anyway, we want to find that only one ideal language, then we should find out what is that only one nation or people who are ideal (more passionate, more romantic, more crazy etc.) lovers on this planet! Does anybody know such a people (nation)? Then probably their language is the best!