If you need any type of character set conversion, you can use recode tool.
It is works for lots of character sets and it is even supports some other operations: converting to base64, quoted-printable, CRLF conversions etc.
You can find a list of conversion options with:
recode -l | less
If you want to change a file’s encoding iso-8859-9 to utf8:
recode ISO-8859-9..UTF8 < example.txt > example.txt.utf8
Or if you want to base64 encode:
recode ../b64 < example.txt > example.txt.b64