Hmm... I'd ask my dad, but he isn't here right now. I know at school we pronounce it Leaf as in Leif (Leaf) Erikson. Umm... I know alittle boy whose name is Leif, and they pronounce it Lafe. So Im not sure, it would depend on the country, and if your not in a Scandinavian country, then it would be whichever you prefer I suppose.