Is cervaza as general a term as beer is or would it be like asking for a lager?
Michael, cerveza is a general term for "beer".
¡Una piña colada con ron, por favor!
What I heard about Spain, they don't ask for beers that way. 'Quiero dos cañas, por favor,' or something like, depending on the kind of beer (or kind of glass, rather), and the region.
"dos cañas" would get you two small draught beers. If you ask for "dos cervezas" you might get any beer - perhaps two bottles of beer - but probably the same!
Beer is uncountable. shortly: two (glass of) beer, please. But on this page US English rules.
Pawe, as soon as you can put a number word in front of a noun to count the noun, it's countable. If you can say "two beer" or "two beers", then "beer" is countable.