Adding support to gnuplot highlighting in kate has been suggested 8 years ago.
However the bug has been marked as "WONT FIX" because no syntax highlighting file was provided.
Now there is one : https://bugs.kde.org/attachment.cgi?id=70366
It should be mandatory to include this in the kate source tree.
I feel there is a need to add manually hand-written syntax highlighter files. Still I didn't find a way to do this.
Thank you for your answer.
I'm awaiting for your comments.
*** This bug has been marked as a duplicate of bug 116064 ***