Does it require to replay game to collect them all?

I'd say, yes, very much so. It's no Avatar: The Last Airbender, that's for sure.

Or you can "cheat" and just trade for stuff with other players.

You need to play for many hours, and i do mean many. And multiple play throughs. But again who the hell would buy this game for the trophies anyhow.

Trophies=/=Enjoyment of a game

I thought you meant how hard the achievements are for the Nintendo DS. ahahahahahahahaha
 
if it only had achievements for it's games... that would be awesome !

I wouldn’ say that they are difficult just very time consuming 

Hard trophies are hard.