What I think you’re looking for is syntax highlighting, which is not contained in the .diff / .patch file, but is added by the tool you’re using to view/edit the patch file. Github adds syntax highlighting to patches when they’re generated by Github, but not when they’re uploaded from other sources, as is the case here.
Any good programmer’s editor should add syntax highlighting to .diff / .patch files. Notepad++ apparently supports this. (I can’t run Notepad++, but see evidence of that on this StackOverflow thread.) If you want syntax highlighting on this change set, you’ll need to open it in an editor that adds syntax highlighting for patches.
Working with a diff/patch toolset is part of the software developer ecosystem and you might find guidance e.g. on StackOverflow.
You’ll get the fix implicitly if you upgrade to OJS 3.x, which is strongly recommended.
I’m afraid that’s all the guidance I can give you on this.
Public Knowledge Project Team