How to make font lock work with comments?

[rusi]

Im hacking on an apl mode


 (let ((st (make-syntax-table))
        (comment-char ?\x235d))
:
:
 (modify-syntax-entry comment-char "<" st)

This char shows as follows (Dont know if it shows elsewhere..)

⍝ A comment

When I put point on the char and call describe-char I get

---------------------------------
        character: ⍝ (9053, #o21535, #x235d)
preferred charset: unicode (Unicode (ISO10646))
       code point: 0x235D
           syntax: <    which means: comment
         category: .:Base
         to input: type "{upshoe-jot}" or "{lamp}" or "{comment}" or
"{@}" with apl-ascii
      buffer code: #xE2 #x8D #x9D
        file code: not encodable by coding system iso-latin-1-unix
          display: by this font (glyph code)
    xft:-unknown-unifont-normal-normal-normal-*-12-*-*-*-d-0-
iso10646-1 (#x2359)
------------------------------

In other words emacs sees this as a comment-type char (similar to what
it says for semicolon in elisp buffers

And yet in an elisp buffer the ; to EOL is red
but here it is not.

Any clues?