Nikolai

Also Finnish, Danish and Norwegian: https://www.nordicnames.de/wiki/Nikolai

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Also Estonian: https://www.stat.ee/nimed/Nikolai

This name was also used among the German minority in Bessarabia: https://ofb.genealogy.net/famreport.php?ofb=krasna&ID=I8253&nachname=George&modus=&lang=de

Also Finnish name. Finnish name day December 6.
https://fi.wikipedia.org/wiki/Nikolai

Also Estonian: https://et.wikipedia.org/wiki/Nikolai

I have twin boys names Bruce Nikolai and Robert Thomas. I absolutely loved the name Nikolai and chose that name for Bruce’s middle name.

Also used in Norwegian, Danish, and Finnish with name days in Finland on December 6 and in Norway on December 6.

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A namesake is
Nikolai William Alexander Frederik, Prins til Danmark (Prince of Denmark), born: August 28th, 1999

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Sources:
Statistisk Sentralbyrå, National statistics office of Norway, http://www.ssb.no
Danmarks Statistik, National statistics office of Denmark, http://www.dst.dk
Väestörekisterikeskus, National Population Register Centre of Finland, http://www.vrk.fi
http://www.nordicnames.de/wiki/Nikolai

Also used in Scandinavia.