Following the discussion in T273705, please add the following to LocalNamesEn.php
qqx - "Display message name".
qqx is a language code in the private use range and the above describes the use made by WMF/Wikidata of this code. Item for the code: Q107239760.
qqq is already working. It displays "Message documentation".
Can you please clarify what this is going to improve/achieve? I'm trying to understand why we need to do this.
It helps identify what the language code is about. Personally, I keep forgetting if it's qqx qqz qzz or whatever.
It should appear at Help:Wikimedia_language_codes/lists/all at "qqx", just below "Message documentation" (for qqq)