I don't think there is a setting for it in the game yet, but it is possible to fix it if you know how a browser works a bit. They really need to add the options menu already...
You will need to open the browser console with the games iframe (might need to look up how you do that, it doesn't work on the nutaku page but only the iframe) and run this bit of javascript: window.set_cookie("lang","en");
It sets your language to english, or another language if you replace the "en" with something else. "fr" to turn it french, in case you want that.