Server side processing unicode problem

Hi all,
I am using datatables server side processing, My table has filter for each column.
User inputs keyword into filter text-box, the keyword will be sent to server then search by that keyword.
There is a problem when user input a unicode into filter.
For instance: user input "nhãn", datatables sends not only:
"n", "nh", "nha", "nhan"
when user types last character "s" to insert diacritical mark, datatables sends the following:
"nha", "nh", "nhãn", "nhã", "nhãn"
It makes the search result incorrect.
I tried to test with some other character, it has similar problem.
Could you help me, thanks you very much.