The documented examples do not work for RST code highlighting.
The <code> tool in the editor creates a .. sourcecode :: python block and that does not render with any highlighting at all.

There are questions on the board with users reporting the same for C as well as Python so this appears to be more than just one language.

Start a new wiki page, set it as a restructuredText markup, insert a code block, either from the example our using the tool. Click "view" and watch it NOT highlight. Click save and watch it render without highlighting.