Remote working this year saved me from the lengthy explanations that accompany my observance of the Jewish High Holidays, Rosh Hashanah and Yom Kippur, which typically fall in late September and early October.
In Japan, usually saying ユダヤ教の休日です (yudayakyō no kyūjitsu desu, they’re Jewish holidays), gets the job done, or maybe I add 大事な (daijina, important) if necessary.
Things get stickier for my Japanese if I have to actually explain what the holidays are. Rosh Hashanah is simply the 新年 (shinnen, new year), so that’s easy, but Yom Kippur is tougher. 去年の罪が神に許されるかどうかの判断の日 (Kyonen no tsumi ga kami ni yurusareru ka dō ka no handan no hi, The day where God decides whether or not you are forgiven for your sins over the past year). 断食をし、朝から夕方までお祈りをしたりする (Danjiki o shi, asa kara yūgata made o-inari o shitari suru, One refrains from eating and prays from morning until dusk).