Ok that should be in - if you view the price trend pages now there are different currency grouping options (with EUR being one of them). Hope this helps!
I can add Spain price trends to PCPartPicker. Quick question though - do you want the price trends to cover just Spanish retailers, or should it trend the prices across all of the EU?
They are US-specific, yes. Thanks for asking that - I'll look into updating those graphs to show for the appropriate region/country depending on what country you've selected (on the top right of the page).
One difference is in compiler optimizations. For a given language, compilers can often make inferences based on the code and the semantics of the language, allowing for very targeted optimizations. If you go from LanguageFoo -> Javascript -> bytecode, then you may be limiting the range of optimizations possible (because Javascript may not be able to infer the same things about the code, be it because of program structure, language semantics, etc.)