Moodle provides a neat tool for admins to customise the strings in the installed language packs. This is the language customisation tool. It is available from:

  site admin -> language 

This is very useful, because you can change strings all over Moodle without touching core code, and the changes are all saved in the database. So they survive a backup,restore,Moodle version upgrade, or server migration. This allows you to customize text across Moodle without needing to write any code at all. 

By default Poodll does not offer the ability to change the language strings that you see in Poodll. But using Moodle's great toolset you can do this.

First, open the language customization tool ..

Then choose the language pack to edit. This will be the language pack that your site or course is using.

Open the language pack for editing

Search for the line(s) of text you wish to change. Once you have found the text you will be able to add an alternate version and save it to the language pack. It might be easier to just select the plugin that you will edit and list all the strings.

Then add your customizations in the local customizations area. When finished all the strings, you should use the "Save changes to language pack" button to save them.

More details on the tool are here: