If you really correctly analyze my Testing eshop and really trying, then you know, that both order was created on one language - on English.
On testing shop are two language - Czech and English and as said Jörgen - The calculation rule uses country not language.
I change only country in cart, that is all - and in product price you must setup VAT - "Apply default rules"
How i display correrct prices in category page and prduct detail page when i dont have czech languge ?
This is other question - I said, if you need change currency on category page and product detail page and change VAT, then you need additional app (for without login) or must be logged.