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.