1. Open the phone settings, as shown:
2. In Settings, select System Settings, and then click Enter.
3. In the system settings, select the keyboard and input method, and then enter.
4. On the keyboard and input method page, click to enter the customized version of sogou input method.
5. In the customized version of sogou input method, select the input settings.
6. In the input settings, slide to the left to close the traditional input button, as shown:
After this setting, your WeChat typing is Chinese, not traditional.