Most of us have grown up and are steeped in American culture: TV, music, movies, books etc... We generally have no problem understanding or using the vernacular, especially those who have travelled a lot, who work with American colleagues or have American friends and partners.
I'll occasionally use American terms here on MR to avoid having to answer questions about what I mean, because the forum is predominantly American. Some of them are closer to what they say in New Zealand anyway... for instance, in the UK, they call a potato chip a 'crisp', in New Zealand they call them potato chips, so it's all much of a muchness.
Although, once on this forum, I was curious enough to query the American use of the word 'golfing' as used as an action verb of golf. In the UK, people will usually say 'I'm going to play golf' rather than 'I'm going golfing'.