1900's - "nineteen hundreds" 1910's - "ninteen tens" 2000 - "two thousand" 2001 - "two thousand and one" 2002 - "two thousand and two" When you get to 2010 and beyond, there is some disagreement. Some people continue saying "two thousand and ten" (2010) "two thousand and eleven" (2011), "two thousand and sixteen" (2016). Other people say "twenty ten" (2010), "twenty eleven" (2011), "twenty sixteen" (2016). Personally I continue with the "two thousand" pronounciation (so "two thousand and sixteen". But I understand why people say "twenty sixteen" because it's a continuation of the pronounciation pre year 2000. i.e "nineteen sixteen" (1916). So you have a choice!

In English, I would say: 1900s - nineteen hundreds 1910s - nineteen tens 1940s - nineteen forties (or "the forties," more casually) 1950s - nineteen fifties (or "the fifties, as above) 2000 - two thousand 2000s - two thousands I know there has been discussion about how to refer to the 2000s. But I think I would continue to pronounce it similar to past decades. "Two thousands" does sound a little strange just because it's relatively new. (Not so new anymore, I guess! :) ) I am not totally sure what the other part of your question refers to. Do you mean more ancient times? If so, I would just pronounce the BC and AD designation (birth of Christ) because that is what we use here typically. Examples: 700 BC = seven hundred BC 300 AD = three hundred AD I'm not sure I've heard someone say simply "in the two hundreds," for example. Just "two hundred BC" or "two hundred AD," depending. However, I'm not very knowledgeable about this. So maybe someone else can address this issue. (native speaker, USA)