How can I stop laughing when I hear a classmate speaking Japanese?

You can pretend not to hear if you don't laugh. Or find something else to do, such as reading books and watching mobile phones. Mainly to distract yourself from caring about others. So I won't laugh. You can also plug your ears so that you won't laugh if you can't hear his voice reading Japanese. There are many practical methods. For example, you can wear headphones to listen to music and read novels. Another question is, is it so ridiculous for others to speak Japanese? You are funny and you love to laugh. Is it your own reason? If so, you should control yourself and distract yourself. You won't laugh.