[ahoge]

From "3. MIME Type Registration of text/csv":

  Common usage of CSV is US-ASCII, but other character sets defined
  by IANA for the "text" tree may be used in conjunction with the
  "charset" parameter.

Basically, you can specify that it's UTF-8 or whatever via the Content-Type response header. Setting this response header isn't something an encoder could do. A CSV parsing library also shouldn't be responsible for loading the CSV file via HTTP. In most cases, CSV files aren't directly fetched via HTTP anyways.

Anyhow, ASCII is utter nonsense. We aren't living in an ASCII world. Even the Americans don't do that. An ASCII-only format is completely useless.