Go doesn’t automatically transform content in the other encodings. You need to check your inputs and the way I’m doing it is like so.

Detect encoding of a file

$ uchardet data.txt
ISO-8859-1
$ file data.txt
data.txt: ISO-8859 text

Converting ISO-8859-1 encoding to UTF-8

curl -s http://maps.natalian.org/data.txt | iconv -f ISO-8859-1 -t UTF-8 > data.txt