utf-8 encoding in URL params

Hi,

I'm accessing a web service API. This API is somehow like convert input string to a graph. this API has a text params. In the specification, this params should be UTF-8 encoded. what shall I do to ensure of this? or just pass the string to it?

The reason I'm asking is, when I pass some Chinese string to that API, some string works fine, some string result in "messy code" in the generated graph.

Any idea?

Cheers, Joe