A zeesn pesakh, mein zun.
Gut Pesach (גוט פסח) = "Good Passover"
In Hebrew you say "chag Sameach"*In English you say "Happy Passover"Unless your friend is over the age of 80, it's unlikely he'd be familiar with the Yiddish greeting. But if that's the case, you can say “A koshern un freilichen Pesach”* (pronounced: A KUH-sher-in OON FRAY-lech-in PAY-sach).*The ch is a guttural sound.
'good Passover' in french is 'bonne Pâque'
The most usual greeting (by English speakers) would be "good yontif." The word yontif is the Yiddish variation of the original Hebrew yom tov, meaning literally good day, but meaning holiday. Others say "chag Pesach sameach" which is Hebrew and means "happy Passover."
Mensch
In Yiddish, you can say "tsayt a gezunt" to say goodbye, which means "stay healthy".
Mazel tov
In Yiddish, "good riddance" can be translated as "אַ גוטע רידנס" (a gute ridnes).
In Yiddish, "good morning" is "gut morgn" (גוט־מאָרגן).
You are a good friend = Du bist a gute Fraind
"Jewish" in Yiddish is "ייִדיש" (yidish), pronounced as "yiddish."