The concept you are proposing will certainly pose a challenge for the UI designers because you will need to reserve twice as much screen space for labels and text.
There are a number of things too take into consideration before going this route.
A non-chinese speaking user can immediately use the site and find the appropriate fields or vice versa.
Important con's to consider:
- The extra screen space needed to accommodate the additional text could be used for content instead. In the end it's the content which creates the value, not the controls and layout to accommodate the content. I'm not sure how this will work out in your case.
- Accessibility: screen readers could have a difficult time using your UI because it's bilingual. Plus, most people using a screen reader be confronted with a language they don't understand. How to tackle that?
- As Pectoralis mentioned, the cognitive load could increase significantly depending on how far you'll take this. A user unable to read one of the two languages will always be burdenend with the extra effort of focussing on the label that he is able to read.
Have you considered to make the first time usage bilingual? In that case users will be able to use the site at first, finding all the appropriate elements and controls without the need to translate. But also make sure that users who need to are able to go all English or Chinese?
In the end, if you don't have a good answer to the con's mentioned, your idea could seriously hinder UX.