When looking at the documentation for Translation#getTranslationForLocale the description for locale says If the translation is not found in the locale of your choice default fall back will be "en" and if not found in "en", then the original value will be returned.

c3ShowFunk(Translation, ‘getTranslationForLocale’)

These seem correct

Translation.getTranslationForLocale('UnknownKey') === 'UnknownKey' 
Translation.getTranslationForLocale('UnknownApp.UnknownKey') === 'UnknownApp.UnknownKey' 


Translation.getTranslationForLocale('UnknownApp.UnknownPage.UnknownKey') === 'UnknownKey'
Translation.getTranslationForLocale('UnknownApp.UnknownPage.UnknownComponent.UnknownKey') === 'UnknownComponent'

How is the key being treated with regards to . delimited keys ?