在GAE Golang Blobstore上处理unicode

Question

I'm trying to upload image to Google App Engine blobstore.
Besides of file field, I have some other fields in the form (such as article title, content...).

I'm using the solution from this answer, it's working fine except error with unicode for those other fields.

For example, "こんにちは" become "$B$3$s$K$A$O(B" when storing to datastore. What is the workaround for this issue?

Updated

Below is my code

   func handleSave(w http.ResponseWriter, r *http.Request) {
      c := appengine.NewContext(r)
      blobs, other_fields, err := blobstore.ParseUpload(r)
      if err != nil {
        serveError(c, w, err)
        return
      }

      id := other_fields["id"][0]
      categoryId, _ := strconv.ParseInt(other_fields["category_id"][0], 10, 64)
      title := string(other_fields["title"][0])
      content := []byte(other_fields["content"][0])

      image := blobs["file"]
      // ...
    }