The release date of the Splatoon 2 for Nintendo Switch still not clear but if you check out the Italian Amazon where you can already pre-order the game you can find the following release date: August 18, 2017.

On the German, US and the Japan Amazon you can’t find it so it maybe a wrong information but Nintendo going to held tomorrow the next Nintendo Direct where they maybe going to announced the officail release date.

Until that you can pre-order it you want but remember, the August 18, 2017 is just a rumor.
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