Yes, that's the customary response.
In French, you would say "Bon shabbat" for Sabbath greetings or "Shabbat shalom" can also be understood in French.
Shabbat shalom is a Jewish greeting which we say during the day of Shabbat. See also:More about the Jewish Shabbat
'Shabbat shalom', which means 'A peaceful Sabbath', is said during Shabbat - sundown Friday to Saturday after twilight.
Shabbat Shalom is a greeting that Jews say to each other on Shabbat (the sabbath). It means "A peaceful Shabbat"
Yes and no. Shabbat Shalom is only said on Fridays and Saturdays.
Yes.
"Shabbat Shalom!"
You can't say Happy Friday in Hebrew, but a common greeting on Friday afternoons is Shabbat Shalom (שבת שלום).
Yes.
You say "Shabbat shalom" right back to them.
Shabbat Shalom (שבת שלום).Note: This means 'A peaceful shabbat'. The phrase "happy shabbat" is not a phrase that is traditionally used.
Only in years where Yom Kippur happens to fall on Shabbat (Saturday). Otherwise, no.