If the localisation of the shop is fr_FR the default-tab will be used and only when you change snippets in shop / fr_FR the new tab will be used. The snippet inhertitance is like this:
shop specific snippets (shop / fr_FR) -> Default snippets from plugin (default /fr_FR) -> German Snippets (default / de_DE)
Every time a snippet is empty in the tab, the next tab will be used.