I use "theatre" because I'm Canadian. "Theater" is considered American English which means that everyone outside of the US points and laughs at Americans for using it.
thats incorrect, the spelling of theater/theatre varies throughout the country in various places, its stereotypical. The same thing is the stereotype that we don't use and don't understand the metric system. The metric system is actually the official standard of measures of the united states, but the united states doesn't enforce it because it would **** with free trade and free speech. I use the metric systems and the old english standard for others. Gallon of milk and gas/2 liter bottle of soda. 100 meter dash, mile jog. etc.
speaking of variants. The pronunciation of "The", i took german and have noticed a pattern between how some people use "thuh", and "thee" subconsciously in English that goes unnoticed. Depending on how many The's are in a sentence they will change the pronunciation. If there is one then it will be "thuh", if there are two it will be "thuh" "thee", if there are three it will be "thuh thee thuh", of course because its subconscious the pattern doesn't always get followed and not everyone picks up on it. If someone really want to emphasis something then they'll say "thee", what else needs to be picked on is the use between the two when switching between different lettered nouns.
quick note on why Soccer isn't called football in the U.S. Before the 1800 the game hadn't been standardized so there were a number of variants. Previously any game with a ball that you kicked was called football regardless of the rules, much like how there are numerous card game variants. The most popular one to get any sort of major league support was the Association Football. Soccer is an abbreviation for Association football. Probably originally pronounced Sosher, but you can't expect people to pronounce everything you print the way its intended.