And then there is this explanation:

Among Latin-speaking Christians, the week beginning with the Feast of the Resurrection was known as "hebdomada alba" (white week), since the newly-baptized Christians were accustomed to wear their white baptismal robes throughout that week. Sometimes the week was referred to simply as "albae." Translaters rendering this into German mistook it for the plural of "alba," meaning "dawn." They accordingly rendered it as EOSTARUM, which is Old High German for "dawn." This gave rise to the form EASTER in English.