<When I took Spanish in high school, there was no attempt to teach us to lisp or make us learn the vosotros form -- in fact, we were told it was mainly an Argentinian thing.>
This belongs in the other forum, but the vosotros form is decidedly not Argentinian. What is in fact Argentinian (or rather, rioplatense, or rather rioplatense/central American) is the "vos" form (2nd person, singular). The "ustedes" form (2nd person, plural) is almost universal in Latin America whereas the "vosotros" form (2nd person, plural) is mostly peninsular.
I wonder if Americans who first learn Latin American Spanish are able to turn on the "lisping", as you call it, without making mistakes. The phoneme /s/ needs to be split into two: /T/ (as in English "thin") for words spelt with "ce, ci, z" and /s/ for all the others (even though a slightly different realization of /s/). If you do not do this from the moment you begin learning the language, you have to rely on spelling and you may end up using /T/ in "casa" and /s/ in "brazo" for example. I know that when I put on a peninsular accent, that's the aspect that requires the most attention, since I do not make the distinction natively.
This belongs in the other forum, but the vosotros form is decidedly not Argentinian. What is in fact Argentinian (or rather, rioplatense, or rather rioplatense/central American) is the "vos" form (2nd person, singular). The "ustedes" form (2nd person, plural) is almost universal in Latin America whereas the "vosotros" form (2nd person, plural) is mostly peninsular.
I wonder if Americans who first learn Latin American Spanish are able to turn on the "lisping", as you call it, without making mistakes. The phoneme /s/ needs to be split into two: /T/ (as in English "thin") for words spelt with "ce, ci, z" and /s/ for all the others (even though a slightly different realization of /s/). If you do not do this from the moment you begin learning the language, you have to rely on spelling and you may end up using /T/ in "casa" and /s/ in "brazo" for example. I know that when I put on a peninsular accent, that's the aspect that requires the most attention, since I do not make the distinction natively.