The confusion with Slovene, Slavian etc. etc. is
also seen in the continental Germanic languages, though to a lesser degree.
English "Dutch" means Netherlandic, Dutch "Duits" means
German, but Dutch "Diets" (uncommon word today) means Dutch, though in
the 17th century "Nederduytsch" meant Dutch; German
"Deutsch" means German, etc. Literally Dutch-Diets-Deutsch means
"clear" (Dutch "duidelijk"; the expression "diets
maken" means "make clear to somebody"), or "the
people's" (ie, said in the people's language, as opposed to
Latin).
Marc