* <https://askubuntu.com/questions/21316/how-can-i-customize-a-system-locale>
* <https://ccollins.wordpress.com/2009/01/06/how-to-change-date-formats-on-ubuntu/>

Used to make lower case abbreviations (mostly for ExifTool)

```bash
$ date +%Y-%b-%d
2020-May-23

$ sudo cp /usr/share/i18n/locales/en_US /usr/share/i18n/locales/en_US-lcase_ab

# Update en_US-lcase_ab

$ diff /usr/share/i18n/locales/en_US /usr/share/i18n/locales/en_US-lcase_ab
```

```diff
80c80
< abday	"Sun";"Mon";"Tue";"Wed";"Thu";"Fri";"Sat"
---
> abday	"sun";"mon";"tue";"wed";"thu";"fri";"sat"
90,95c90,95
< abmon	"Jan";"Feb";/
< 	"Mar";"Apr";/
< 	"May";"Jun";/
< 	"Jul";"Aug";/
< 	"Sep";"Oct";/
< 	"Nov";"Dec"
---
> abmon	"jan";"feb";/
> 	"mar";"apr";/
> 	"may";"jun";/
> 	"jul";"aug";/
> 	"sep";"oct";/
> 	"nov";"dec"
```

Install and use

```
$ sudo localedef -f UTF-8 -i en_US-lcase_ab en_US-lcase_ab.UTF-8

$ LC_TIME=en_US-lcase_ab.UTF-8 date +%Y-%b-%d
2020-may-23
```

Apparently the names are slightly different when reported by `locale`.
However, still failing in Perl when trying both ways.

```sh
$ locale -a | rg en_US
en_US
en_US.iso88591
en_US-lcase_ab.utf8
en_US.utf8

$ LC_TIME=en_US-lcase_ab.UTF-8 exiftool ...
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
	LANGUAGE = (unset),
	LC_ALL = (unset),
	LC_TIME = "en_US.lcase_ab.UTF-8",
	LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_US.UTF-8").

$ LC_TIME=en_US-lcase_ab.utf8 exiftool ...
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
	LANGUAGE = (unset),
	LC_ALL = (unset),
	LC_TIME = "en_US.lcase_ab.utf8",
	LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_US.UTF-8").
```