BaseGameText and LocalizedText are indeed as Gedemon said in their own seperated Database which cannot be accessed from the Databases where <UpdateDatabase> actions are sent.
All you can do from an <UpdateDatabase> action is re-direct which LOC_SOMETHING the game should use for the "Name" field (for example) for a given District, Building, Unit, etc. But you cannot access the contents of what is in LOC_SOMETHING for its Text field.