“请不要跟贴。多谢”is ridiculous. You can choose not to speak here. If you choose to, you should let others voice as well.

‘To use English, or not to’ can be a free choice, even though in most cases it still reflects a speaker’s consciousness and taste. To me, it is always better to use Chinese if the vast majority audiences are Chinese or the state presence of China is prominent. Among Chinese professors in US, some like to use Chinese in an international meeting hosted in China and some don’t. Nevertheless, if you observe them carefully, you can easily find some interesting differences between them in many perspectives. There are many kinds of us no matter you like it or not. Getting along with people who don't share your basic principles is difficult and is a virtue.