translations: add setting language selection and related strings

.config/quickshell/ii/Translation.qml

@@ -84,7 +84,7 @@ Singleton {
     function getLanguageCode() {
         var configLang = "auto"
         try {
-            configLang = ConfigOptions.language.ui
+            configLang = Config.options.language.ui
         } catch (e) {
             configLang = "auto"
         }

.config/quickshell/ii/modules/common/Config.qml

@@ -215,6 +215,7 @@ Singleton {
             }
 
             property JsonObject language: JsonObject {
+                property string ui: "auto" // UI language. "auto" for system locale, or specific language code like "zh_CN", "en_US"
                 property JsonObject translator: JsonObject {
                     property string engine: "auto" // Run `trans -list-engines` for available engines. auto should use google
                     property string targetLanguage: "auto" // Run `trans -list-all` for available languages

.config/quickshell/ii/modules/settings/InterfaceConfig.qml

@@ -465,4 +465,74 @@ ContentPage {
             }
         }        
     }
+        ContentSection {
+        title: Translation.tr("Language")
+
+        ContentSubsection {
+            title: Translation.tr("Interface Language")
+            tooltip: Translation.tr("Select the language for the user interface.\n\"Auto\" will use your system's locale.")
+
+            ConfigSelectionArray {
+                id: languageSelector
+                currentValue: Config.options.language.ui
+                configOptionName: "language.ui"
+                onSelected: newValue => {
+                    Config.options.language.ui = newValue;
+                    reloadNotice.visible = true;
+                }
+                options: {
+                    var baseOptions = [
+                        {
+                            displayName: Translation.tr("Auto (System)"),
+                            value: "auto"
+                        }
+                    ];
+                    
+                    // Generate language options from available languages
+                    // Intl.DisplayNames is not used. Show the language code with underscore replaced by hyphen.
+                    for (var i = 0; i < Translation.availableLanguages.length; i++) {
+                        var lang = Translation.availableLanguages[i];
+                        var displayName = lang.replace('_', '-');
+                        baseOptions.push({ displayName: displayName, value: lang });
+                    }
+                    
+                    return baseOptions;
+                }
+            }
+
+            Rectangle {
+                id: reloadNotice
+                visible: false
+                Layout.fillWidth: true
+                Layout.topMargin: 8
+                height: noticeText.implicitHeight + 16
+                radius: 8
+                color: Appearance.m3colors.m3secondaryContainer
+                border.color: Appearance.m3colors.m3outline
+                border.width: 1
+
+                Row {
+                    anchors.fill: parent
+                    anchors.margins: 8
+                    spacing: 8
+
+                    MaterialSymbol {
+                        anchors.verticalCenter: parent.verticalCenter
+                        text: "info"
+                        iconSize: 20
+                        color: Appearance.m3colors.m3onSecondaryContainer
+                    }
+
+                    StyledText {
+                        id: noticeText
+                        anchors.verticalCenter: parent.verticalCenter
+                        width: parent.width - 36
+                        text: Translation.tr("Language setting saved. Please restart the quickshell to apply the new language.")
+                        color: Appearance.m3colors.m3onSecondaryContainer
+                        wrapMode: Text.WordWrap
+                    }
+                }
+            }
+        }
+    }
 }

.config/quickshell/translations/zh_CN.json

@@ -393,5 +393,10 @@
   "Lap": "计时",
   "Welcome app": "欢迎应用",
   "Corner style": "角落样式",
-  "Bar layout": "条栏布局"
+  "Bar layout": "条栏布局",
+  "Language": "语言",
+  "Select the language for the user interface.\n\"Auto\" will use your system's locale.": "选择用户界面的语言。\n\"自动\" 将使用系统语言环境。",
+  "Language setting saved. Please restart the quickshell to apply the new language.": "语言设置已保存。请重启 quickshell 以应用新语言。",
+  "Auto (System)": "自动（系统）",
+  "Interface Language": "界面语言"
 }