Some cats are just naturally vocal, and some cats talk a lot for months or even years and then suddenly simply stop talking. I find Turkish Van mixes talk more than most regular tabbies, but sometimes it seems like all the cats have begun to immitate each other, so that they all make the same sounds when they want something or are saying hello -- sort of like learning a local dialect. Since my dogs also do that -- the rescue of a single hound gave me an uneven chorus of howling and singing dogs who had never used that vocalization before -- I become more and more convinced that when animals are reared in free-ranging groups they develop certain similar ways of vocalizing and doing things -- again, just like humans with their traditional basket weaves, their shared recipes that become regional specialities, and their dialectical differences from the "outside" world.
Like a good mommy, you learn to listen to them and identify distress, hunger, greetings, anger, fear. As your own babies train you to listen to their early cries, so you learn to identify when a cat is terrified or in distress, or if they are just passing the time of day. Personally I love it when a cat comes in the window and says "prrrup" at me before going to the food dish.