"No, il tuo piatto è completamente diverso."

Translation: No, your dish is completely different.

[Marninger]

How do I know when "piatto" means dish and when it means plate?

[wolf1mtb]

No worries. You will know the difference when it is used in the context of a conversation. DL does not provide such context. Either 'dish' or 'plate' is a correct answer because no context was given to whether the statement was referring to china (plate) or what was placed upon that china (dish/food).

[SDL_1987]

I don't understand why completamente can't be translated as "totally" and well as "completely" and "entirely".

[Marninger]

Well, it probably can be translated that way, - but it does mean completely.

[tango-alpha]

Why is "non" wrong?

[Lloydo3000]

'Non' is more like 'not.'

[carmenacoto]

"Non" goes before verbs: "Non mangio carote", and "no" before everything else: "No, your dish is..."

[xyphax]

Magenta gives a good guideline for use ... also
no = no
non = not, not, neither, etc.
'non' can take on meaning when used with other words ... if you wish to go deeper, check out this site on the double and triple negatives in Italian!
http://italian.about.com/library/fare/blfare141a.htm

[Volizione]

Could "differente" be used here instead of "diverso" or no?

[aph-italia]

When did this conversation happen? Why did this conversation happen?

[garbagehead]

Plate not correct. It should be, as in different plates (one with a pattern, one without a pattern) or colloquially in English, the plate (it's a tasty plate of food) is the same as the dish (it's a tasty dish of food).