To wish someone a happy Rosh Hashanah, the most common and traditional greetings are in Hebrew, expressing wishes for a good and sweet new year. Here are some ways to say it:

• "Shanah Tovah" (שנה טובה): This means "Good year" and is akin to saying "Happy New Year."
• "Shanah Tovah Umetukah" (שנה טובה ומתוקה): This extends the wish to "A good and sweet year."
• "L’Shanah Tovah" (לשנה טובה): A variant meaning "For a good year."
• A longer formal greeting is "L’shanah tovah tikatevu vetechatemu" (לשנה טובה תכתבו ותחתמו), meaning "May you be inscribed and sealed for a good and sweet year."
• "Chag Sameach" (חג שמח) means "Happy holiday" and can be used during Rosh Hashanah as well.
• In Yiddish, "A zis gebentsht yor" means "A sweet year filled with blessings."

For a simple, respectful greeting in English, saying "Happy Rosh Hashanah" or "Happy New Year" is also appropriate and appreciated, especially if you are not fluent in Hebrew. Common wishes often include references to sweetness (like honey) and blessings for health, peace, and happiness in the coming year. Examples:

• "Shanah Tovah Umetukah! May this New Year bring you countless blessings and sweet moments."
• "Wishing you a joyous Rosh Hashanah filled with peace and happiness."
• "May your year be as sweet as honey."

These greetings work well for friends, family, colleagues, or acquaintances observing the holiday.