Add Simplified Chinese as a system language

The installer asks for the language before the keyboard, and
Setup > Language (omarchy language en|zh) switches it later. Under
zh_CN the menu reads its labels from omarchy-menu.zh-cn.jsonc, the
shell from I18nZh.js through I18n.tr, and notifications are worded
by their sender through omarchy-text, which reads the same table.
User text is never translated.

shell/Commons/Tr.js

@@ -0,0 +1,24 @@
+.pragma library
+.import "I18nZh.js" as Zh
+
+// Shell text in the session's language; QML reaches this through the I18n singleton, plain JS imports it.
+var chinese = Qt.locale().name.indexOf("zh_CN") === 0
+
+function tr(text) {
+  var args = arguments
+  var template = chinese && Object.prototype.hasOwnProperty.call(Zh.table, text) ? Zh.table[text] : text
+  // One pass, so an argument that itself contains %2 stays as given.
+  return String(template).replace(/%(\d)/g, function(match, n) {
+    return n > 0 && n < args.length ? String(args[n]) : match
+  })
+}
+
+// Text a panel's own model builds in known formats: the first matching template is translated with what %1.. captured.
+function trMatch(text, templates) {
+  for (var i = 0; i < templates.length; i++) {
+    var pattern = "^" + templates[i].replace(/[.*+?^${}()|[\]\\]/g, "\\$&").replace(/%\d/g, "(.+)") + "$"
+    var match = String(text).match(new RegExp(pattern))
+    if (match) return tr.apply(null, [templates[i]].concat(match.slice(1)))
+  }
+  return tr(text)
+}