Missing Serbian/sr language file #741
Description
It seems there's a non-Latin flavor of Serbian defined in the RelativeFormatterLanguage but the file itself is missing.
If I'm understanding correctly, tableForLocale will return a RelativeFormatterLanguage even though there's no language present. I'm assuming we should avoid having a case for languages that don't exist so we can attempt to load a fallback.
This might cause #720 to happen. I'll look into opening a PR soon.