Thank you for contacting WPML Support. You can achieve it by doing below steps:
1. Go to WPML >> Languages >> Edit Languages.
2. Add EN / 中文 in Translation text boxes as you can see in the attached screenshot.
3. Edit the language switcher settings from WPML >> Languages > Menu language switcher and set the similar options as you can see in the attached screenshot.
Please let me know if this resolves your issue or you need further assistance with this issue.