NixOS: How to granularly configure locale settings? - locale

Question

On my home laptop running NixOS 19.03, in /etc/nixos/configuration.nix, I use the default locale settings:
i18n = {
consoleFont = "Lat2-Terminus16";
consoleKeyMap = "us";
defaultLocale = "en_US.UTF-8";
};
That's the only way I know to control locale settings in NixOS, and it's too broad. I want more granular control, so that I can use a mixture of US English and Colombian Spanish. (That's a consequence of my job, not a personal choice.) Specifically, I need these settings:
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=es_CO.UTF-8
LC_TIME=es_CO.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=es_CO.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=es_CO.UTF-8
LC_NAME=es_CO.UTF-8
LC_ADDRESS=es_CO.UTF-8
LC_TELEPHONE=es_CO.UTF-8
LC_MEASUREMENT=es_CO.UTF-8
LC_IDENTIFICATION=es_CO.UTF-8
LC_ALL=
On my work desktop (running Ubuntu 18.04), if I evaluate locale in bash, that's what I see. On my home NixOS system, each of those variables is either set to US English or nothing:
[jeff#jbb-dell:~/nix-jbb]$ locale
LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=
I thought maybe I should edit /etc/locale.conf, copying the settings from my work system into it. But when (on the NixOS system) I print that file to screen, it doesn't include any of the above variables except LANG:
[jeff#jbb-dell:~/nix-jbb]$ cat /etc/locale.conf
LANG=en_US.UTF-8
[jeff#jbb-dell:~/nix-jbb]$
Therefore the other variables, like LC_NUMERIC, must be getting set somewhere else. I'm worried that if I edit /etc/locale.conf I'll break my system. Is editing that file the right way to set granular locale information in NixOS? And if not, what is?

Answer 1

The option i18n.extralocalesettings is where to set those. E.g.:
i18n.extraLocaleSettings = {
LC_MESSAGES = "en_US.UTF-8";
LC_TIME = "de_DE.UTF-8";
}

Answer 2

I have never seen a NixOS setting for that, but I guess you can work around that with:
services.xserver.displayManager = {
sessionCommands = ''
export LC_NUMERIC=es_CO.UTF-8
export LC_TIME=es_CO.UTF-8
export LC_MONETARY=es_CO.UTF-8
export LC_PAPER=es_CO.UTF-8
export LC_NAME=es_CO.UTF-8
export LC_ADDRESS=es_CO.UTF-8
export LC_TELEPHONE=es_CO.UTF-8
export LC_MEASUREMENT=es_CO.UTF-8
export LC_IDENTIFICATION=es_CO.UTF-8
'';
};
This should work for all your local (graphical) sessions. If you access this computer with ssh as well, you might add the same exports also to ~/.bashrc
If you don't want to have the setting for all users, you can also add the exports to ~/.xession instead of /etc/nixos/configuration.nix as shown above.