feat(keyboard): add modes for languages

configs/keyboard.nix

@@ -4,13 +4,20 @@
   ...
 }: let
   commaSep = builtins.concatStringsSep ",";
+  languages = {
+    de = "T3";
+    gr = "polytonic";
+    ru = "phonetic";
+    ara = "buckwalter";
+  };
+  defaultLanguage = "de";
 in {
   # man 7 xkeyboard-config
   services.xserver = {
-    layout = commaSep ["de" "gr" "ru" "ara"];
+    layout = commaSep (builtins.attrNames languages);
     # T3: https://upload.wikimedia.org/wikipedia/commons/a/a9/German-Keyboard-Layout-T3-Version1-large.png
     # buckwalter: http://www.qamus.org/transliteration.htm
-    xkbVariant = commaSep ["T3" "polytonic" "phonetic" "buckwalter"];
+    xkbVariant = commaSep (builtins.attrValues languages);
     xkbOptions =
       commaSep ["compose:caps" "terminate:ctrl_alt_bksp" "grp:ctrls_toggle"];
     libinput.enable = true;
@@ -18,6 +25,14 @@ in {
 
   console.keyMap = "de";
 
+  environment.systemPackages =
+    lib.mapAttrsToList
+    (language: variant:
+      pkgs.writers.writeDashBin "kb-${language}" ''
+        ${pkgs.xlibs.setxkbmap}/bin/setxkbmap ${defaultLanguage},${language} ${languages.${defaultLanguage}},${variant}
+      '')
+    languages;
+
   # improve held key rate
   services.xserver.displayManager.sessionCommands = "${pkgs.xorg.xset}/bin/xset r rate 300 50";