Shop URL comes with an extra "amp;"

Revised

I found a problem comes from the system, we have 3 languages in our website, default is English. The other 2 to be Traditional Chinese and Simplified Chinese.
* Need to add 223.223.216.3 bri-star.com in host file.

Main page:
http://bri-star.com/wordpress/

After click the Traditional Chinese button at top right hand corner, it goes to
http://bri-star.com/wordpress/?lang=hk accordingly.

And then I click 購物 (Shop) on the menu, it goes to
http://bri-star.com/wordpress/?post_type=product& amp;lang=hk rather than
http://bri-star.com/wordpress/?post_type=product&lang=hk
While http://bri-star.com/wordpress/?post_type=product&lang=hk is English version of Shop page.

I can’t find any method to turn it back to normal, thanks.

Best Regards,
William