Write happy day in greek to English language?

The phrase "happy day" doesn't have a single perfect equivalent in Greek that captures the nuance of the English expression. The best translation depends on the context. Here are a few options:

* Καλή μέρα (Kali mera): This translates literally to "good day" and is a common greeting, appropriate for a happy day, but it doesn't explicitly *say* "happy day."

* Χαρούμενη μέρα (Harouménī mera): This translates more literally to "happy day" and is perfectly acceptable.

* Ωραία μέρα! (Oraia mera!): This translates to "beautiful day!" or "lovely day!" and emphasizes the pleasantness of the day.

* Καλημέρα! (Kalimera!): This is a more informal version of "good morning" and could be used if the happy day is in the morning.

So, depending on the specific situation, any of these could work. Χαρούμενη μέρα (Harouménī mera) is probably the closest direct translation.