Just searched about this question and came here! But I found few results which may helpful to others.
Tamil - South Indian language - 247 letters.
Chinese contains more than 10000 but those are considered as pictures cannot counted as letters
I didn't know but was bored.. It's apparently either Khmer (Cambodian) with 74 letters or Thai with 76(?)
Hmm don't really know that answer but i know that english has more than portuguese, there's no k, w or y.