As of 5.0, the preferred way to format a date/time is
lc_time_fmt datetime fmt [ locale ]
where fmt is one of these:
%c FDCC-set's appropriate date and time
representation.
%q Long date without weekday
%Q Long date with weekday
%x FDCC-set's appropriate date representation.
%X FDCC-set's appropriate time representation.
If you use one of these formats, it is automatically localized to the user's selected locale.
Anybody who knows what FDCC stands for is welcome to chime in.