How to Encode/Decode double encoded string.

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks

I have below string,

whereas in one instance i have below two encoded strings of the above string,

this is a test international 脿谩芒盲
This one is getting encoded properly to utf8 using module encode utf8 function.
this is a test international 锟斤拷锟斤拷
This one gives ??? in the diamond like chars using module encode utf8 function.

It seems that in this instance string is getting double encoded, how we can handle this to work in both the instances.

Thank you.