[Rd] Setting LC_CTYPE=en_US.UTF-8 failed

[Steven Penny]

Using this in my "~/.profile":

    export LC_ALL=en_US.UTF-8

Yields this:

    $ Rscript -e 'print(9)'
    During startup - Warning message:
    Setting LC_CTYPE=en_US.UTF-8 failed
    [1] 9

This is confusing as the exact same environment works fine with other
languages:

    $ python3 -c 'print(9)'
    9

    $ ruby -e 'puts 9'
    9