Hey, There is a bug (or a feature, depends on how you see it) in mediawiki extension namespace registration [1]. If an extension registers a namespace, there is no way to override that. It can be problematic in cases when there is a conflict of IDs between two installed extensions or one extension and custom-defined namespaces. We want to change that but there are several approaches and each of them has benefits and issues:
One (suggested by me) is to make IDs of namespaces registered by extension configurable using LocalSettings.php. This allows us to easily "move" a namespace without needing to touch other configurations related to that namespace but it also adds a global variable and also can't handle conflict in names of namespaces.
Another approach (suggested by legoktm) is to skip registering a namespace from extensions when the namespace constant is already defined. This doesn't have problems that the first approach has but you need to duplicate the configuration when there is a conflict.
Please contribute at the discussion and add your comments/concerns. Also feel free to suggest a new approach.
[1]: https://phabricator.wikimedia.org/T160462
Best