"Language code" is a predefined property that represents a BCP47 formatted language code and is provided by Semantic MediaWiki. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.
The database is currently locked to new entries and other modifications, probably for routine database maintenance, after which it will be back to normal.
The system administrator who locked it offered this explanation: The wiki is under maintenance. Das Wiki wird derzeit gewartet.
