Use index.md as the main page within a chapter

style guide ref:
https://docs.civicrm.org/dev/en/latest/documentation/style-guide/#hackable-urls

docs/standards/php.md

@@ -116,7 +116,7 @@ $string = ts("Membership for %1 has been updated. The membership End Date is %2.
 ));
 ```
 
-For more information on translation, see [Translation for Developers](/translation/developers.md).
+For more information on translation, see [Translation for Developers](/translation/index.md).
 
 ## Scope
 

mkdocs.yml

@@ -240,7 +240,7 @@ pages:
   - UI Reference: framework/ui.md
   - Upgrade Reference: framework/upgrade.md
 - Translation:
-  - Translation for Developers: translation/developers.md
+  - Translation: translation/index.md
   - Extensions Translation: translation/extensions.md
   - Database localized fields and upgrades: translation/database.md
 - Standards: