"That is Croatian!"
Now I understand the hesitation: He gave me western spelling because a westerner could not be expected to recognise his native Cyrillic spelling. I hope I haven't caused offence. I find "Српски" ("Srpski") and stare at the new text in confusion matched only by the lifeguard's happy recognition as I slowly puzzle out a few Germanic or Russian-like words.
"Of course!", I find myself explaining. "Serbian letters are nearly the same as Russian." He looks even more puzzled. "Well, not really, this here, I guess it's a long 'l'?"
"Yes. But Russian?"
"It's the same as Greek. Well, nearly. Close enough. I was a mathematician." It's mostly intelligent guesswork anyway.
"It is very different." The native speaker hadn't really considered the similarity, and says he cannot read Greek at all, but for someone who reads Cyrillic as slowly as I do, he is willing to admit some approximation. He starts teaching me words, and I mentally file them under "Generic Linguistic Hints for Russia and the Middle East".