The formatting is largely oblivious to locale. The reason for this is that
certain dates in certain calendars are not POSIX-compliant and the system
functions necessary for locale information thus do not work consistently. The
main exception to this is the (abbreviated) names of months (bB), which
could be useful for pretty printing in the local language. For separators and
other locale-specific adornments, use local knowledge instead of depending on
system locale settings; e.g. specify %m/%d/%Y instead of %D.
Week information, including weekday names, is not supported at all as a
"week" is not defined for non-standard CF calendars and not generally useful
for climate projection data. If you are working with observed data and want
to get pretty week formats, use the as_timestamp() function to generate
POSIXct timestamps (observed data generally uses a standard calendar) and
then use the base::format() function which supports the full set of
specifiers.