glibc 2.27 introduced new format specifiers for the month names.
It's obligatory to use them in several languages already and it's
encouraged to use them for all languages because it is not destructive
for any language. As more languages are expected to follow this
standard it's better to use the "%OB" format specifier now so it will
start working correctly automatically.
See also: https://sourceware.org/bugzilla/show_bug.cgi?id=10871
This standard has been also working in BSD and OS X since 1990s,
if anyone tries to use gnome-shell in these systems.
Note: This will not work correctly with glibc < 2.27, there is no
detection whether the system is old or new.
https://bugzilla.gnome.org/show_bug.cgi?id=780957
a647445b95