How does this sound?
Some remarks:
- This should not be a separate Special:GadgetPreferences but part of Special:Preferences in Gadgets section, when entire usage of one particular tool can be toggled. If this tool is activated, the preferences GUI should appear immediately below (and vanish if toggled off).
- The JSON spec should be subpage like MediaWiki:Gadget-myTool/preferences.json, while site configuration might be MediaWiki:Gadget-myTool.json and implementation is at MediaWiki:Gadget-myTool.js
- Texts do need localization mechanism. A global root may contain English, French, Japanese and German, and on Commons users will expect their user language. Further translations need to be added easily by global collection of local languages.