I believe that if you move to a new country, you should learn the language. Even if you can't do the French accent or German throat thing, and you mess up on the gender and verb conjugation, just attempting to communicate with the people is important. Do WE mind when someone comes to the US with an accent or gets their words mixed up or uses a native expression? No. It's cute, or funny, or sometimes profound.
I agree to a certain extent about adopting the vocabulary here in Britain, but I don't worry about it too much or get paranoid about it. People here have said they love my accent and they quite enjoy my American terms. Though I have had a lot of British terms make themselves at home in my speech (and now sometimes forget the American equivalent!), I've spent many years using American words and can't just stop using them overnight, nor should I feel I have to. (e.g. I've always called it a "restroom"; I hate the word "toilet".) If someone doesn't understand me the first time, I use another term they do understand. No biggie. Those who complain about American words or the American spell check on their computers need to get a life.
The way they use punctuation here does seem quite erratic, so I just use the punctuation I was taught. Especially when it comes to commas, colons, and semicolons. Punctuation was created to assist the reader, so any form that makes the text clearer is best. I think schools in the US and Britain have really been slacking on the grammar and punctuation. It just kills me when I see an official news item with errors - "then" instead of "than", "their" instead of "they're"....
We bought a cheap digital camera and the owner's manual is a hoot! It must have been translated by someone's cousin who speaks a little English. "Please do not put the batteries into fire to prevent explosion to cause. "
Cracks me up.
And New Year's Eve I learned a new Scottish word - numpty. Means idiot. As in "I felt like a real numpty trying to Highland Fling in stilettos."