* מזל טוב (mazel tov) - This is the most common and versatile phrase, used for a variety of occasions, including good luck. It literally means "good fortune" or "congratulations."
* אַ גוט געזעל (a gut gezelt) - This is a more formal way to say "good luck," literally meaning "a good journey." It's often used for someone starting a new venture or undertaking a difficult task.
* אַ גוטע וואָך (a gute vokh) - This means "a good week" and is used for wishing someone good luck for the coming week.
* האָב אַ גוטע צייט (hob a gute tzeit) - This means "have a good time" and can be used for wishing someone good luck in a more casual setting.
It's important to note that Yiddish is a very expressive language and the best way to say "good luck" will depend on the specific situation.