Maybe it will get cooler in Paris now that France couldn't beat South Korea...
But seriously, there are many differences in slang, but not too many differences in idioms, such as 'once in a blue moon'.
The problem with slang and idioms is that they come in and out of use. The dictionaries of idioms that you see seem to try their best to catalogue every single one, no matter how obscure. I've definitely had cases of students picking out and using idioms that went out of fashion twenty years ago. It's disheartening for them to be corrected because they thought they were doing a good thing.
For up-to-date idioms, (I remember once we discussed 'sup dawg?) I suggest that you look at sites like this:
http://www.macmillandictionary.com/2005/index.htm
Also a great source of idioms is basically any comedy, as they rely a lot on puns. You'll never teach your students all the idioms, so it's a good idea to teach them to recognise them and guess the meaning from context.