Shabbat (שבת) is the Hebrew word for ceasing or stopping
שפרה.
They're called Shabbat candles (Neirot Shabbat in Hebrew).
Shabbat comes from the Hebrew word for sit/rest. Shabbat is the day of rest.
The plural form of "Shabbat" is "Shabbatot" in Hebrew.
"Shabbat" is the usual spelling in English of the Hebrew word for sabbath.
The Sabbath day of rest is called shabbat in Hebrew.
You can't say Happy Friday in Hebrew, but a common greeting on Friday afternoons is Shabbat Shalom (שבת שלום).
Shabbat (Hebrew for 'Sabbath') begins slightly before sunset on Friday afternoon, and ends after twilight on Saturday night.
In French, you would say "Bon shabbat" for Sabbath greetings or "Shabbat shalom" can also be understood in French.
They're called Shabbat candles (in English); neirot Shabbat (in Hebrew); or Shabbes Licht (in Yiddish).
The most polite response would be to wish the person a "Shabbat shalom" in return. It's like wishing someone a nice weekend.