Sometimes, Debian installations have some troubles with locales when you're using apt for example. It is caused by missing environment variables or missing locales configuration.

To fix this problem for ever, just do these two things :

Add these lines on .bashrc or .zshrc :

export LANGUAGE=en_US.UTF-8
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8

Then you can run these commands :

locale-gen en_US.UTF-8
dpkg-reconfigure locales

The last command ask you to choose any locale, I use en_US.UTF-8 in my case.
You need to restart your shell to apply your environment variables.

The problem is fixed !