Here are what we have in Greek:
"γιορτη" το celebrate a particular event. e.g. Someone's name day, in fact we often just say "ειναι η γιόρτη του" for it is "his name day" rather than "ονομαστικη γιορτη" e.g.
"δεξίωση" as in reception "δεξίωση γάμου"
"πανηγύρι" a mass celebration which may include the whole town/village and border on a fun fair, usually to celebrate the feast day of the local church.
"γλέντι" a lively party
and of course "παρτυ".
Check out the images for ***πανηγύρι" :)
γιορτη is a tricky one alright ! I tried "fiesta" (transplanting an element from the other end of the Med) but it was rejected, reasonably enough. The explanations above are excellent, thanks for that; "celebration" I like. But "feast" is only used if you're roasting swans and malmsey is being poured by serving wenches. I suppose the most British thing would be to say "I'll see you at the do tonight".
Graecophones usually say "γιορτή" for "feast", "celebration" and "πάρτυ" for "party". e.g. You will never hear anyone say "γιορτή γενεθλίων" for "birthday party" but you will hear many say "πάρτυ γενεθλίων" ;) What's more, you can hold a party to celebrate something, a birthday, a wedding anniversary, a promotion, etc. in which case it is both γιορτή (celebration) and πάρτυ, but you can also have one just for the fun of it! In this case you can't say γιορτή, just πάρτυ.
While not wrong, why not follow the structure of the original sentence with 'tonight' at the end? It is possible that, because of the flexibility of Greek syntax, not all valid translations have been added to the database, but the obvious one that matches best the given phrase will definitely be accepted. :)