You can change your Forum language by updating your "User Profile"
Click on the small icon (top right) that looks like a person Then click on "Board Preferences"
You will then see an option for "My language" - you can change this to your preferred language.
Note this will only change the main Forum descriptions and help information, it will not change the text of the postings. If you want to translate the text of postings, most browsers have an option to translate pages into another language.
I hope that helps!