How to install Notepad++ PZS syntax highlight plugin
Download the latest version from: https://github.com/ibrrus/npp-pzs/blob/master/PZS.xml
Open Notepad++
Open the User Defined Language Dialog e.g. via Language > Define your language ....
Press the Import ... button and select the downloaded file.
Open Project Zomboid script file and select Language > PZS.