Christos voskrese, which means Christ has Risen, is the Easter greeting in Church Slavonic which brings the response Voistinu voskrese or Indeed, He has risen.
Easter, of course, celebrates the Resurrection of the Lord Jesus and the salvation of Man.
The date for Easter is the Sunday following the first full moon after the spring equinox, which is always reckoned, regardless of astronomical observations, to be March 21 as per the Western churches that use the Gregorian calendar, so Easter always falls between March 22 and April 25 so the holiday is a late one this year.
The dating for Easter correlates with the means the Jews use to set the date for Passover, which correlates with Scripture since Scripture indicates that the Crucifixion of the Lord occurred as the lambs were being slaughtered for the celebration of that holiday.
In fact, in most Western languages the the name for the day is a cognate of the Pesach which is the Hebrew name for Passover. In Latin it would be Pascha so Paschal lamb would be Passover lamb.
In English and German, the word comes from Eostre month, which was basically April, and which the pagans who spoke Germanic languages had named for the goddess Eostre.
In Slavic, the holiday is called “Great Night” (Velikonoce in Slovak) or “Great Day” (Velikden in Ukrainian).
There are some caveats regarding the date. The Eastern churches that use the Julian calendar set the equinox is set at April 3, and, of course, the spring equinox is based on that of the Northern Hemisphere.
So, Christos Voskrese.
Voistinu voskrese
Every country has own traditions of celebrating Easter!