Aren't the Czechs partially Bavarian, though mixing.
Their old name was Boii and while they used that name they were very close to the original form of ethnic name, Ser-boi (Serboi). With time `Ser` was lost and even more later local designation `Czech` prevailed.
to tell you frankly, we are all Sarmatians, SRBI (or form SRBIJANCI). Just, Lusatian and Balkan Serbs keep using (in possible original form) that once universal name of all Proto Slavs. Many others (Poles among them) adopted local ethnic designation- Polani but still preserved memory on their Sarmatian past/origin.
Words `Bavarian`, `Barbarian`, `Boika`, `Boii` are probably of same origin. For `Boii` we know that coming from `Serboi`, as linguistics confirms. See, Serboi is nothing but SRBI (Serbs, Serbians), original form of Sarmatians/Sarmats. Those words `Bavarian`, `Barbarian`, `Boika`,.. semas to be shortened terms of Sarmatia (i mean, original word Sarmatia- `Serbia`; actually- SRBIJA).
Confusion coming from fact that Greek and Roman authors couldn`t pronounce that SRB and they soften that with form SRM, inserting even `a` SARM.
But, speaking of our ultimate past, we are all RAS narod (people)- foreign designation was Thracians (Th-racians),.. /Roman version was `Traci`/,.. /Byzantine version was Triballi/,../Slovak-Hungarian (Panonian) version was `Raci`/,.. /Polish version was `Racowie`/,../Russian version is `Rusi` and it is still in use. Form SRB (Sarmats) appeared on historical scene later, with higher level of social organization and on the higher level of diversification of language. Still, it is possible that ethnic designations based on the roots RAS/SRB existed parallel from the time of immemorial and that even form SRB could be older- primordial. i would later speak more of it in one other thread.