How do you say happy Easter in Japanese?

Japan does not celebrate Easter, but you could say:

復活祭おめでとうございます (fukkatsu-sai omedetō gozaimasu)

イースターおめでとうございます (īsutā omedetō gozaimasu)

Answer

In Japan, we do not celebrate Easter so we do not have the exact Word to say "Happy Easter" but most of the Japanese understand if you say "Easter." If you want to translate to Japanse it is 復活祭 (hukkatsusai) but since we do not celebrate, may be the closest phrase will be "復活祭 おめでとう" (hukkatusai omedetou). It still sounds little strange to me as a Japanese though...