tlmgr update --all

[Karl Berry]

    > Is it necessary to set LANG as well? The same problem appeared in many
    > other programs and setting LC_ALL=C was sufficient.

Technically LANGUAGE (specific to GNU gettext) should be unset to
guarantee that LC_ALL takes effect, although I suspect few people use
LANGUAGE.

https://www.gnu.org/software/gettext/manual/gettext.html#Locale-Environment-Variables
and the following section
https://www.gnu.org/software/gettext/manual/gettext.html#The-LANGUAGE-variable

karl