Dead Cells can be played in these languages : 

French, German, English, Traditional Chinese, Korean, Spanish, Italian, Japanese, Polish, Portuguese, Russian, Turkish

You can change it by going in the Settings>Language

If you want to play in Simplified Chinese, we have teamed up with bilibili for the release of Dead Cells mobile in China. You can find all information about the Chinese version such as pre-registration here : https://game.bilibili.com/deadcells/.