Seems you’re saying unwritten languages don’t exist.
NO ALPHABET? Chinese has no alphabet. Neither does Japanese. Get thee to a liberry. Look up syllabary, logographhic writing, pictography...
Croatian got codified when Ljudevit Gaj adapted Vuk Stefanovuc Karadzic’s system.
My M.A. specialization is in Mediaeval Latin: there was no no single (codified) standard, but plenty of literature and many regional languages. —This doesn't have to be boring: get a CD of Carl Orff’s CARMINA BURANA (GOOGLE THAT). Fun music. The music is from the 1930s, the song texts (spring time, love making, satire of king and pope, drinking) are in mediaeval Latin and mediaeval German. Germans, too, had no standard (codified) language before Luther's Saxon dialect (Upper Silesian) dialect was adopted by the hundreds of German principalities as a lingua franca. — That was once Frankish, subsequently any international languge. So the plan is like “Vlachs, Valachi”, who were many diverse nationalities that were not German or Hungarian. Today's Franks are the Holland Dutch who kept the old language. In Gallia (called France today, though it isn't Frankish anymore) the Franks dropped Frankish and now use the Francien neo-Latin dialect of the region. Along this track, in Serbia there is Fruska Gora, which originally meant ‘Frankish mountain /woods’. (Which “Franks”?)
When is Dio going to explain “Vlach” to us? I'll keep my calendar open.