Locales for non-Gregorian calendars

[Avid Seeker]

This discussion has probably been had before, but I noticed glibc
definitions of LC_TIME only cover Gregorian month names:

```
LC_TIME
% Abbreviated weekday names (%a)
% Full weekday names (%A)
% Abbreviated month names (%b)
% Full month names (%B)
% Equivalent of AM PM
% Appropriate date and time representation
d_t_fmt     "%d %b، %Y %I:%M:%S %p"
% Appropriate date and time representation for date(1)
date_fmt    "%d %b، %Y %Z %I:%M:%S %p"
% Appropriate date representation
d_fmt       "%d %b، %Y"
% Appropriate time representation
t_fmt       "%Z %I:%M:%S %p"
% Appropriate 12 h time representation (%r)
t_fmt_ampm  "%Z %I:%M:%S %p"
week 7;19971130;1
first_weekday 2
END LC_TIME
```

However, Unicode ICU4J include definitions for an extensive set of
calendars: Islamic, Hebrew, Coptic, etc.

https://unicode-org.github.io/icu-docs/apidoc/dev/icu4j/com/ibm/icu/util/Calendar.html

What's the current progress on integrating that with glibc to have
similar locale formats but for other dates? This is especially relevant
since many countries don't have Gregorian as the official calendar, and
so a big part of the locale is missing by not including the other
calendars.

Thanks,
Avid