This is a good experiment, but a bit flaws. "That's so off the chain!" is an incredibly American only expression. It may be said in Canada, but fat chance it'll be said in the UK, NZ or Australia or other English majority countries. Arguably, "fat chance" also falls into this dilemma. The test is more accurate when you stick to grammatically correct, syntax adherent sentences that avoid any national inflections that won't properly translate to another language.For kicks and giggles, try entering a phrase in GT and translate it to German. Then copy that translation in and translate it to French, followed by Italian, and then Spanish. You should then be able to translate the final phrase back into English, identical to what you first entered.
This is one of my favorite results:
That's so off the chain! ---------> For this by its cover!
Here's another example:
Bee's Knees = Works fine in a lot of countries, but doesn't translate well into other languages or requires far more words to express itself correctly.
Here's something that's fairly old and mainly UK based:
Easy peasy lemon squeezy.
Say that in the US and you'll get strange looks. Say it in German and you may find yourself institutionalized.