feat(i18n): Implement and refine language selection feature

Introduces a language selection option in settings, allowing users to manually choose an application language or revert to automatic system locale detection. This includes UI updates, settings integration, and improved language detection logic.

Modules/Settings/Tabs/GeneralTab.qml

@@ -204,13 +204,19 @@ ColumnLayout {
       Layout.fillWidth: true
       label: I18n.tr("settings.general.language.select.label")
       description: I18n.tr("settings.general.language.select.description")
-      model: I18n.availableLanguages.map(function(langCode) {
+      model: [
+        { "key": "", "name": I18n.tr("settings.general.language.select.auto-detect") + " (" + I18n.systemDetectedLangCode + ")" }
+      ].concat(I18n.availableLanguages.map(function(langCode) {
         return { "key": langCode, "name": langCode }
-      })
-      currentKey: Settings.data.general.language !== "" ? Settings.data.general.language : I18n.langCode
+      }))
+      currentKey: Settings.data.general.language
       onSelected: key => {
         Settings.data.general.language = key
-        I18n.setLanguage(key)
+        if (key === "") {
+          I18n.detectLanguage() // Re-detect system language if "Automatic" is selected
+        } else {
+          I18n.setLanguage(key) // Set specific language
+        }
       }
     }
   }