Hello.
They should have a very short description on the right tab of the PPM. If you mean a good and in depth description then you should google the program.
NLS means Native Support Language... For example, my main language is es_ES spanish. My puppy is in spanish, but if i download i.e XFE it'll be in english, so if the program has a traduction, there will be also a NLS package so i install that, it'll detect my main language, and translate it to spanish. If your language is english then i don't think you should care about it.
In your example i'd have to download
opera-12.02-s.pet
opera_NLS-12.02-s.pet