SO where did all the slavic eastern European jews come from again?
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The Slavic languages are spoken in Eastern and Central Europe and include Russian, Ukrainian, Serbian, Polish, Czech, Bulgarian, and similar tongues.
“Slavonic,” as used in this article, denotes the Slavic dialect that Cyril and Methodius used for their mission and literary work. Some today use the terms “Old Slavonic” or “Old Church Slavonic.” Linguists agree that there was no single common language spoken by the Slavs in the ninth century C.E.[Box on page 29
https://wol.jw.org/en/wol/d/r1/lp-e/2001166