You are right about Belgium, which only turned into a federal state (and apparently continues to do so) during the last few decades. I was under the impression that this had happened shortly after WW2.
In Germany, three of the states call themself "Republic". These are Bavaria, Thuringia and Saxony. The term they use is "Freistaat", a word created in order to find a "Germanic" equivalent for the Latin/French "republic". During the Weimar Republic, most Länder called themselves a Freistaat (including Prussia), after 1945, the term has fallen out of favour in most states which only define themselves as a "Land".
And isn't the reason Bavaria, Thuringia, and Saxony call themselves such is because they were the only Weimar states remaining, with the others being mediatized after 1945?
And on topic: Czechoslovakia could be more viable if Slovaks had a feeling of more parity in the state. The Czech lands (i.e., Bohemia, Moravia, and Czech Silesia) had the bulk of the industry and infrastructure. By contrast, Slovakia, which did not come into its own as a political entity until very recently (not counting its time as a Third Reich puppet), was more rural and subject to Magyarization.