training site messages not translated

Training site messages like "upgrading soldier evade from level 0 to level 1" shown when hover on that site cannot be translated. Corresponding messages for production sites can be translated as expected.

Widelands version: bzr8668
Platform: Debian testing

In the beginning of constructor of TrainingSiteDescr class (src/logic/map_objects/tribes/trainingsite.cc), the second argument to the parent class constructor which seems to be a message context is empty. I guess it is the cause of this issue.

   : ProductionSiteDescr(init_descname, "", MapObjectType::TRAININGSITE, table, egbase),

If I modify the second argument like this:

   : ProductionSiteDescr(init_descname, table.get_string("msgctxt"), MapObjectType::TRAININGSITE, table, egbase),

the training site messages are translated as expected.