It is not common or standard to say "Happy Yom Kippur" because Yom Kippur is a solemn day of fasting and repentance. Instead, appropriate traditional greetings include:
- "Gmar Chatima Tovah" (גְּמַר חֲתִימָה טוֹבָה), meaning "a good final sealing," referring to the belief that one’s fate is sealed for the coming year on Yom Kippur.
- A shortened version is "Gmar Tov" (גְּמַר טוֹב), meaning "a good seal."
- "Tzom Kal" (צוֹם קַל), meaning "an easy fast," wishing someone an easy fast on this day.
- "Shanah Tovah" (שָׁנָה טוֹבָה), meaning "good year," is also common but more typical for Rosh Hashanah, the Jewish New Year.
So, while you wouldn't typically say "happy Yom Kippur," you could say [גמר חתימה טובה](javascript:void(0)) (Gmar Chatima Tovah) or [צום קל](javascript:void(0)) (Tzom Kal) as respectful and meaningful greetings for Yom Kippur observance.