Expressing wishes or situation which did not actually happen in the past:
I would have done something ...
is translated as condicional compuesto in the book I'm using:
Habría hecho algo ...
Similarly, 3. conditional has the following structure:
si + pluscuamperfecto de subjuntivo + condicional compuesto
Si hubiera hecho algo, habría pasado otra cosa.
However, based on my observations in Guatemala and various Latin American countries, it seems these two sentences are very often, if not always, expressed as:
Hubiera hecho algo ...
Si hubiera hecho algo, hubiera pasado otra cosa.
Sometimes, to avoid repetition, one part of the conditional uses the -ese form:
Si hubiera hecho algo, hubiese pasado otra cosa.
As an example from right now, a quotation from 'El señor de los cielos':
Para mi no hubiera sido suficiente haber matado a ese desgraciado.
I think it would also be correct to say:
Para mi no habría sido ...
as I think this is what my book preaches.
Is this something specific to latin america, is it some high order grammar I just haven't learned yet, or maybe just one of those things that are not grammatically correct but the way people generally speak?
Also, this seems to happen just for the past and 3. conditional; 2. conditional (the part without the 'si') and current hypothetical situations always use condicional simple and can't use subjuntivo (imperfecto or whatever):
Yo haría esto ...
Si fuera rico, viajaría por el mundo.
Yo hiciera esto ...
Si fuera rico, viajara por el mundo.