Notice the use of the word "unnaturally". I am not talking about calling the trunk of your car "the boot" , or referring to underwear as "pants". These translation are actually necessary when moving to a new country as the use of the familiar American term can cause confusion.
What I am talking about is mostly slang or words that you have never used in your American life before moving to the UK.
Case in point, taken directly from an ex-pat forum when speaking about the sweet dish often eaten after one's evening meal:
"I didn't need any seconds tonight. Had lunch at a pub and was well full after tea!"
Really? C'mon. What you mean is that you didn't need any DESSERT. You had lunch at a pub and were VERY full after DINNER. Why oh why do people do this? Especially when your audience is mostly American?? Not to mention that saying "well full" makes you sound like an idiot. It is one of those words/phrases that no American, no matter how long they have been living in Britain cannot say without making a dick out of themselves. Others include: bloody and chuffed. Any Americans who use these words are forcing it and should be slapped.
Although my example above gets at least one point for using the terms correctly, which is more than can be said for at least one other ex-pat I know. I saw a status on an ex-pat's Facebook not long ago that said "I really should be cleaning the house, but I just cant be asked". Oh dear. Certainly you mean: I just can't be arsed which is a slangy way of saying you can't be bothered?
Words fail me.
My unsolicited advice: don't try so hard and if you must, make sure you get it right. Even a quick Google search of the word or phrase you think you have learned will save you from looking like a fool.