RE: Alt has to be short ...

Even for a specific language, there might not be hard and fast
rules. I'd say the cut-off limit between ALT and LONGDESC
should be written into site-specific guidelines, and consistently
adhered to on a per-site basis. But yes, the shorter the better
And speaking of languages, I'd guess something like finnish
would end up being quite long...but that's based on my very
limited knowledge of that language, so disregard ;-)
 
Patrick