Names of content models can be localised by defining the message content-model-$model, which is used by ContentHandler::getLocalizedName, and gets shown in various interface messages, notably in Special:ChangeContentModel.
However, for cases where the model id includes uppercase characters (like in Scribunto, MassMessageListContent, GadgetDefinition, etc), adding the message causes the grunt-banana-checker build to fail. Example: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/MassMessage/+/1005982
Proposed solution: modify ContentHandler::getLocalizedName to use the message content-model- .. strtolower( $model ) instead.