I had trouble today on a client site using my MySQL power tools Maatkit and Statpack.

$ ~/scripts/statpack.py --files=mysql.status.091015.080001.txt,mysql.status.091015.090001.txt
Traceback (most recent call last):
  File "/home/rbradfor/scripts/statpack.py", line 563, in ?
    main()
  File "/home/rbradfor/scripts/statpack.py", line 527, in main
    locale.setlocale(locale.LC_NUMERIC, '')
  File "/usr/lib64/python2.4/locale.py", line 381, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

$ cat /var/log/slow-query.log | ./mk-query-digest
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
	LANGUAGE = (unset),
	LC_ALL = (unset),
	LANG = "e_US"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

I tracked a difference in the LANG environment variable with what is on another production server. Changing it addressed the problem, however I suspect a more underlying OS related problem that I did not have time to address.

$ env
...
LANG=e_US
...
$ export LANG=en_US.UTF-8

I didn’t track the source of e_US, en_US also worked.