How to switch language in fish shell?

Question

I tried to switch languages in fish (eg. French as shell supports it) using sudo dpkg-reconfigure locales, but nothing changed.
Exporting LANG variable doing set --global --export LANG fr_FR.UTF-8 and launching child fish instance had no effect too. locale output is:

LANG=fr_FR.UTF-8
LANGUAGE=
LC_CTYPE="fr_FR.UTF-8"
LC_NUMERIC="fr_FR.UTF-8"
LC_TIME="fr_FR.UTF-8"
LC_COLLATE="fr_FR.UTF-8"
LC_MONETARY="fr_FR.UTF-8"
LC_MESSAGES="fr_FR.UTF-8"
LC_PAPER="fr_FR.UTF-8"
LC_NAME="fr_FR.UTF-8"
LC_ADDRESS="fr_FR.UTF-8"
LC_TELEPHONE="fr_FR.UTF-8"
LC_MEASUREMENT="fr_FR.UTF-8"
LC_IDENTIFICATION="fr_FR.UTF-8"
LC_ALL=

What actions are required to change fish-shell language?

Answer 1

Exploring related questions I found the solution: set the environment variable in ~/.config/fish/config.fish. So the first line of that config file may be set --global --export LANG fr_FR.UTF-8.
But it is still not clear to me why this approach works in contrast to the tried...