Fix #10154 and #10090: locale normalizes the UTF-8 encoding to "UTF-8" instead of...

Fix #10154 and #10090: locale normalizes the UTF-8 encoding to "UTF-8" instead of "UTF8"

On MacOSX and OpenBSD (and possibly other BSDs) "en_US.UTF-8" is a valid locale
while "en_US.UTF8" is not. As the former works on Linux as well it is better
to normalize to that value.