Is there any thing to convert string encording?

[nalaginrut]

In ruby, we can use force_encoding to convert the encoding of a string:
"abc\u{6666}".force_encoding("UTF-8")

What's the same thing in Guile?

PS: I know Guile treat all strings with "UTF-8". I don't mean to encode
UTF-8 string. I need something like "force_encoding".