solution. I looked like this:
(defvar dired-re-month-and-time
(concat
(let ((language (getenv "LANG")))
(cond
((equal language "es_ES")
"
\\(ene\\|feb\\|mar\\|abr\\|may\\|jun\\|jul\\|ago\\|sep\\|oct\\|nov\\|dic\\)")
(t "
\\(Jan\\|Feb\\|Mar\\|Apr\\|May\\|June?\\|July?\\|Aug\\|Sep\\|Oct\\|Nov\\|Dec\\)")))
; June and July are for HP-UX 9.0
Env vars are global, and defvar is evaluated once. I had a mixture of machines with
different languages that I accessed through efs, so I had to create a superset.
/J. Haglund