If your preferred language is other than English, you'd probably like to have the cal command in you own language. To do this, replace the English name of the days using a sed expression, and include it in an alias in your .tcshrc file. For French, it is:
alias cal "cal | sed 's/ S M Tu W Th F S/Di Lu Ma Me Je Ve Sa/'"Now when you run cal, you'll actually be running the alias, and it will replace the English dates with your language's versions.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030615091356873