I think I found something..:
I just searched for the word "Domingo" in the entire ca-es language pack and found:
So please have a look at the translations in that file.
Also: Please note that form JEM 2.2.3 onwards, the Afax Calendar module will be obsolete. Ajax functionality is now incorporated in the standard calendar module that installs with the standard JEM package.
If you make any corrections we would appreciate if you add them in our Transifex language pack repository.