Obviously of those lanugages that use an alphabet. I read in yahoo answers that Khmer (Cambodian) has 74 letters in its alphabet, but you can’t really take Yahoo Answers as a final source 
I also realize there may be dispute as to what is a seperate letter and what is a just one letter with a mark above it
It would probably help in answering you which one of these two options you were looking for.
You’re probably going to have to qualify “alphabet.” I’ll assume you’re excluding syllabaries and going with systems that are more-or-less one character to one sound: the language with the most phonemes is !Xù (spelled variously), with over 100. Different sources range from 102 to 112.
According to the Handbook of Scripts and Alphabets Cambodian is a syllabary. It gives 33 consonants and 21 vowels for Cambodian, and of course those vowels are essentially diacritics added to the consonants. So (1) it’s not an alphabet strictu sensu and (2) I don’t see how they get 74. Cherokee has 84 different symbols. It’s not an alphabet either but would seem to count if Cambodian does. Off to count more alphabets, back in a minute.
For purely alphabetic scripts, it looks like Old Church Slavonic is the one to beat at 43.
А Б В Г Д Е Ж Ѕ З И І К Л М Н О П Р С Т Ѹ Ф Х У Ц Ч Ш Щ Ъ Ы Ь Ѣ Ю Я Ѥ Ѧ Ѫ Ѩ Ѭ Ѯ Ѱ Ѳ Ѵ
a b v g d e zh dj sh i i k l m n o p r s t u f kh o ts ch sht u y i e yu ya ye e[sup]n[/sup] a[sup]n[/sup] ye[sup]n[/sup] ya[sup]n[/sup] ks ps th y
(I snuck a modern я in there because I couldn’t find the appropriate character in my font. They’ll probably all display as little squares anyway.)
ETA: The transcribed alphabet below isn’t very helpful, it’s just to give the general idea.
I got 'em all. Firefox 3.0.12, English (United States).
I guess I don’t know. I mean in German are the letters u and ü, the same letter or not? I dont know.
They aren’t taught as separate letters at the college level for students just learning the language.
For living languages, Yakut, a.k.a. Sakha, has 40 characters, the standard Cyrillic crowd plus a few additional ones. Wikipedia I count д and дь as separate letters, much like ll and l in Welsh or Spanish, because even though дь is a digraph it’s a distinctly different sound, not just a palatalized version of the same one as in Russian.
(One of the characters doesn’t display when I pull it up, but it looks like the love child of a capital F and a 5: imagine the lower horizontal stroke of the F curving down like the round part of the 5. Ҕ ҕ.)
I’ve always heard it called the Cambodian alphabet myself.
The Thai alphabet has 44 consonants and 15 vowel symbols.
Nor in high school, in fact we were told NOT to think of them like that, but rather as a shorthand for ue (oe and ae), as well as thinking of the esszet as simply ss.
Which is in fact historically correct: the two dots (¨)are a highly reduced superscript form of the Roman cursive [e], and the ß is old “long s” (the thing that looks like a lowercase f without the crossbar) run together with s. ſ + s = ß. (I love unicode.)
Cherokee has 85.
Any advance on 85?
Cherokee is a syllabary, rather than a phonetic alphabet. If you are going to allow syllabaries, try that used to represent Yi:
Vai has a syllabary with a large number of symbols, also - in excess of 150 (the table of 152 symbols isn’t complete):
We may wish to restrict ourselves to phonetic alphabets.
I suspect the criterion for “separate letterhood” is whether it is treated by a dictionary as such. For example, I believe that French vowels are alphabetized each in one sequence whether they are written with accents or not. In contrast, Russian ë (yoh sound) is a distinct letter from Russian e (yeh sound). Though a digraph, I believe ll is considered a distinct letter in both Welsh and Spanish, as in the latter is ñ. (In English, however, llama comes in the same sequence as other l- words, between liver and lobster. In Spanish, however, it would be part of a new sequence following luz.
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In Spanish, ll and rr used to be considered separate letters (they’re separate phonemes), but currently they’re not. Ñ is considered a separate letter; accented vowels are considered… accented vowels (so, not separate letters).
The Catalans avoid the question of whether ç is a separate letter; it’s not part of the alphabet as recited and it doesn’t get a dictionary grouping, but there’s no words that start with ç and it is a distinct, uh, spelling entity (Barça isn’t the same as Barsa; the first one is correct spelling, the second one is acceptable only if the means you’re using for writing don’t let you write a ç).
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In what sense is a syllabary not a kind of alphabet? You’ve got a set of symbols, each of which represents a sound, which you can put together to make words.
Some scripts (such as Hindi) have a default vowel for each consonant letter. If the letter is followed by a different vowel or no vowel at all, then a diacritical is added or two consonants are formed into a ligature. Another term for such a script is abugida.
According to the Wiki article on Alphabet,
A syllabary is different than an alphabet in that an alphabet’s symbols are used to represent one sound at a time whereas a syllabary’s symbols represent an entire syllable, not just “a sound.” An abjad is similar to an alphabet but lacks vowels.
If you’re so inclined, you might want to scour up a copy of Writing Systems of the World, by Akira Nakanishi.
Another useful resource (but not available at the moment) is www.omniglot.com.
Monty- great answer!
Thanks, DrDeth. Given my degree is in Linguistics, you probably guessed already I’m interested in this stuff.
The bolded part is kind of indeterminate:
Ё is definitely used in teaching materials and in children’s books and such. And in many Cyrillic-alphabet charts, you’ll see ё listed separately. But I wonder if when a native Russian speaker writes down the Cyrillic alphabet, he/she is likely to include ё.
FWIW, a quick perusal of pravda.ru didn’t reveal any usages of ё at all on the front page and in the several articles I went through.