A:AnswerYou will! The buffalo pocket plushie is one of the two goodies packed in with the Premium Edition, the other being a cloth poster! It's not a pre-order bonus, just part of what's included in the Premium Edition (you would not get it even if you pre-ordered the Standard Edition).
A:AnswerThe DLC is not included in any physical releases of the game (whether preordered or not) and will need to be purchased. It is unknown if the DLC will be available to purchase via any means other than directly from the Switch eShop. It is also unknown if a physical version with the DLC will ever be released, but that has not been the case with past Story of Seasons games.
A:AnswerThe only available languages for the US (and I think EU) release are English, Spanish, French, and German! So Simplified Chinese is not available, and to my knowledge, not planned. I don't know about the languages for other region releases.