To change the language in Planet Coaster, please follow these steps:
1) Go to your Steam Library and find Planet Coaster in the bar on the left. Right-click on Planet Coaster and then choose Properties (outlined in blue in the image below.)
2) The Properties box will now have opened. Please go to Language (outlined in blue in the image below).
3) Click on the arrow to bring up a list of the languages you can play Planet Coaster in, and select the one you'd like. Then press close. 
Your game should now start in your chosen language, but if you're still running into issues, please feel free to raise a support ticket with us:
