Created attachment 102975 [details] simple html test case Setting the '-webkit-locale' property to a language by JavaScript fails without any warning or error thrown. It works for the value 'auto', thus. See attached test-case. (Test 3 fails, 'de' is expected.)
Locale identifiers are not CSS value keywords (like auto is). If you're using this syntax, you need to quote the identifier so that it's treated as a string, e.g. '"de"'.
Thanks! Looks scary…