PanelApp, as documented on blade-samples, displays its localization key instead of the name in the panel (see screenshot) 

Until 7.3, it was not necessary to override getLabel(Locale locale) - with 7.4 it's necessary.

This seems to be related to the changed implementation of BasePanelApp.getLabel(Locale), which also looks like something else was intended:

Master, as of today when I file this issue:

(e.g.: If the first call to LanguageUtil.get failed, let's log an exception and call it again to reveal the result)

My best guess is that either the first or the second LanguageUtil.get call should have survived from the old implementation in 7.3, e.g.

The old implementation actually still would work. As of 7.4, translations are centralized, so they're loaded from a global module - but not for custom PanelApp implementations. It makes sense to change the order of lookups, but not to eliminate the local lookup and try the failing global one twice.