If you're an American like me, you might find European foreign language education, well, foreign. There, it starts very young - often at age 6. My German cousin, for example, was fluent in French and English by age 12 - b/c she was taught her academic subjects in French or English (spoken by native speakers) starting at 6 years old. She also had English servants in the house, whom she would have heard since babyhood.
As an aristocrat, Almasy would've had an English governess or tutor. He was a member of the Royal Geographical Society - it's quite possible he attended Oxford or Cambridge. It's not surprising he'd speak perfect British English. His French and German were probably also at the same level or close to.
Ralph's accent in Schindler's List was perfectly German.
I think he also can convincingly play Americans.
This was intentionally aristocratic English with a slight intonation, as he's a Hungarian Count who grew up attending British boarding schools.