Add language switching utility function

types.ts

@@ -121,6 +121,9 @@ export interface To {
    * @see: {@link https://karabiner-elements.pqrs.org/docs/json/complex-modifications-manipulator-definition/to/software_function/iokit_power_management_sleep_system/}
    */
   software_function?: SoftwareFunction;
+  select_input_source?: {
+    language: string;
+  };
 }
 
 export interface MouseKey {

utils.ts

@@ -211,3 +211,19 @@ export function rectangle(name: string): LayerCommand {
 export function app(name: string): LayerCommand {
   return open(`-a '${name}.app'`);
 }
+
+/**
+ * Shortcut for "switching to a language" command
+ */
+export function switchToLanguage(languageCode: string): LayerCommand {
+  return {
+    to: [
+      {
+        select_input_source: {
+          language: languageCode,
+        },
+      },
+    ],
+    description: `Switch keyboard language to ${languageCode}`,
+  };
+}