Traduko - Greka-Urduo - Καλως ήρθες

This is ONLY for singular.

If one addresses more than one person or wants to be polite (like the use of plural for one person in French) it's Καλως ήρθατε

Alternative translations:
Καλώς όρισες
Καλώς ορίσατε

Welcome as a noun : Καλωσόρισμα, υποδοχή