catopen ?-fail|-nofail? catname
              Open  the  message  catalog catname.  This may be a
              relative path name, in which case the NLSPATH envi-
              ronment  variable  is  searched to find an absolute
              path to the message catalog.  A handle in the  form
              msgcatN is returned.  Normally, errors are ignored,
              and in the case of a failed call to catopen, a han-
              dle  is  returned  to  an unopened message catalog.
              (This handle may still be  passed  to  catgets  and
              catclose,  causing  catgets  to  simply  return the
              default string, as described above.  If  the  -fail
              option  is  specified,  an error is returned if the
              open  fails.   The  option  -nofail  specifies  the
              default  behavior  of  not  returning an error when
              catopen fails to open a specified message  catalog.
              If  the  handle  from a failed catopen is passed to
              catgets, the default string is returned.

              This command is provided by Extended Tcl.