Both Alibaba and 1688 are safe platforms as measures are taken to ensure the quality of the suppliers and that buyers are safe. 
However, Alibaba is safer between both platforms because it is a much bigger platform. Plus, they feature trade assurance and gold assurance

1688 lacks any form of Alibaba’s Trade Assurance. So, if you want to add an extra layer of security, look for a sourcing agent.
 It is the recommended step if you want a reliable supplier.

Chinese suppliers in 1688 only supported payments in RBM(CNY). 
If you want to pay, you have to convert the funds to the accepted currency and make the transfer
You can also contact a buying agent, which will help handle these hassles. 

You can translate the contents of 1688.com to English by opting for the Chrome auto-translate extension from the Chrome store. 
Once you download the extension, add it to Chrome.
This way, every time you visit 1688.com, a pop-up suggests you convert it to English.

Alibaba offers easier shopping than 1688 for international orders. 
Alibaba aims to serve the international market, so they are equipped with the right tools.