We were going to make a universal pronunciation guide a while ago, but that quickly petered out. I guess I'll just give a few basic tips that are more or less applicable everywhere.
The thing that differentiates English orthography from most other Latin orthographies (especially transliterations, for obvious reasons) is that they are almost entirely consistent—given almost any written word, it can be accurately pronounced. Sometimes the rules for a given language can be quite opaque
, but they exist. (Some possible exceptions: Swedish, Danish, although I doubt anyone will be pissed if moderators don't lilt and make guttural sounds properly.)
The key, I guess, to reading things legibly and quickly is to break them down into syllables. Aztec may seem daunting at first, but when you break it down into syllables, you can see that its syllable structure is really just (C)V(C). Of course, long words can be tough to break down on the fly; I like to facilitate this in questions I write by breaking it down into syllables with interpuncts, like so: Tla·huiz·cal·pan·tecuh·tli.* These won't always be there, and sometimes a pause will be necessary regardless, but as long as it's not too long, it's not a problem.
Depending on how long these sessions are, it may be instructive to go through the languages one is most likely to encounter in questions—French, German, possibly Chinese, Japanese, Italian, and Spanish—and get these down. The latter two, especially aren't hard at all, and it's silly and pernicious for a moderator to swallow up a foreign word so that nobody can understand them. For less common languages, I'd just try and have your mods adhere to the general rules above and to use common sense. Chances are, the player won't know how to pronounce the words either. Some languages, like Russian, are objectively harder to approximate for English speakers, but them's the breaks.
A note on science: People suck at reading scientific terms, myself included. Fortunately, most of them are systematically constructed from a given set of pre-, suf-, and I guess infixes. Going through some of the more common ones could be helpful, so that moderators leave the "poi" out of topoisomerase.
This may also be a useful resource: www.forvo.com
* "Tecuh" is one syllable in Aztec. This is what you get when Spaniards try and fit their system to a foreign language. I should also note that Nahuatl orthography isn't really that consistent—long vowels aren't marked. This, however, is irrelevant for quizbowl, where an understandable approximation is the aim. This is one reason why diacritics needn't be retained by any means.