I'm glad that you like Downtown Abbey, and I agree that the Dowager is joy to watch. The language in Downton Abbey is very close indeed to the English spoken in Britain today. In fact, almost all the dialogue is in modern English, with a few old-fashioned phrases thrown in to give it a period flavour. The servants sometimes use regional Yorkshire expressions. If you have any specific vocabulary or expressions that you want to ask about, please do.

Speaking as someone from New Zealand, I would say that the speech they use is easy to understand, with very little that isn't familiar. The English we use here is based on British, so that probably helps. We typically watch a range of programs, and read a range of books, some of which are historical, so we are familiar with the language. That probably also means that we don't notice the use of older terms as much as you might. But - it definitely does have a particular style - being both a little old-fashioned, and particularly that it is very 'upper class', which has a particular style of its own. We would only use that style, and some of those expressions if we were deliberately trying to sound old-fashioned, and snobby.