Change directory for Kate syntax highlighting files

I'm running Standard Debian Wheezy with KDE 4.8.4 and Kate 3.8.4.

The Kate text editor's syntax highlighting files are located in:

/usr/share/kde4/apps/katepart/syntax

If I run

kde4-config --prefix

this gives

/usr

and $KDEDIR is empty. This results in that only XML files in the upper direcory are used for highlighting.

In several other forums, I saw that it should work to create a folder "syntax" in

~/.kde/share/apps/katepart/ If I put syntax-highlighting files there on my system, they appear to be ignored. How can someone change/set the directory for the syntax-highlighting files used by *Kate* to an arbitrary directory?