This issue occurs for all versions of HPS and is caused by adding new content into translation files being used by HPS. For example in the latest HPS a new command was added thus requiring new content in the translation files such as cmdExampleCommandExplaination = I am the explanation for the new command

People that have already run HPS previously and have the language files generated will run into the error if they update to the HPS version with the new content and run said new command.

The area causing the issue is located in localisation which can be seen here.
In more programmatic terms issue happens when
activeLang.getProperty(key) == null && defaultLang.getProperty(key) == null
because the local version of the server owner's translation files wont have an update

Proposed solution:

• Make updater that adds in missing paths for the default language file