Issue in Posting Chinese Characters to "Web to lead form"

Issue in Posting Chinese Characters to "Web to lead form"

We are posting data from our ASP.net application to Zoho "Web to lead form". When we post Chinese/Japanese characters, data in Zoho shows garbled characters.
We have tried it by changing Content-type, charset etc. but no success.

What should we do to post Chinese/Japanese characters to Zoho "Web to lead form"? Kindly assist.