Comment by thenickdude

Or else edit /usr/lib/x86_64-linux-gnu/gconv/gconv-modules and comment out this section:

  #       from                    to                      module          cost
  alias  ISO2022CNEXT//          ISO-2022-CN-EXT//
  module ISO-2022-CN-EXT//       INTERNAL                ISO-2022-CN-EXT 1
  module INTERNAL                ISO-2022-CN-EXT//       ISO-2022-CN-EXT 1

Then run "iconvconfig" to rebuild the iconv cache. This disables that charset completely.