dev: add en_GB locale archive to devenv

Provide a Nix glibc locale archive with en_GB.UTF-8 so tools inside the devenv shell inherit a valid UTF-8 locale.

devenv.nix

@@ -6,16 +6,33 @@
 }: let
   system = pkgs.stdenv.system;
   pkgs-unstable = inputs.nixpkgs-unstable.legacyPackages.${system};
+  hasGlibcLocales = pkgs.stdenv.hostPlatform.isLinux && pkgs.stdenv.hostPlatform.isGnu;
+  devLocales =
+    if hasGlibcLocales
+    then
+      pkgs.glibcLocales.override {
+        allLocales = false;
+        locales = [
+          "en_GB.UTF-8/UTF-8"
+          "en_US.UTF-8/UTF-8"
+        ];
+      }
+    else null;
 in {
   # https://devenv.sh/basics/
-  env = {
-    # Parallel deps compilation
-    MIX_OS_DEPS_COMPILE_PARTITION_COUNT = 8;
-    # Enable JS/LV debugging (required?)
-    NODE_ENV = "development";
-    # Delay npm dependency resolution to reduce rushed supply-chain updates.
-    NPM_CONFIG_MIN_RELEASE_AGE = "7";
-  };
+  env =
+    {
+      LANG = "en_GB.UTF-8";
+      # Parallel deps compilation
+      MIX_OS_DEPS_COMPILE_PARTITION_COUNT = 8;
+      # Enable JS/LV debugging (required?)
+      NODE_ENV = "development";
+      # Delay npm dependency resolution to reduce rushed supply-chain updates.
+      NPM_CONFIG_MIN_RELEASE_AGE = "7";
+    }
+    // lib.optionalAttrs hasGlibcLocales {
+      LOCALE_ARCHIVE = "${devLocales}/lib/locale/locale-archive";
+    };
 
   # https://devenv.sh/packages/
   packages = with pkgs;