Locale switch (#200)

* Add function to set app locale

* Setting for selecting app language

- Adds requirement for "flutter_localized_locales"
- Change main app to stateless

* Reload entire app tree when language is changed

* Update release notes

* linting

lib/settings/app_settings.dart

@@ -1,8 +1,12 @@
 
 import "package:flutter/material.dart";
 import "package:font_awesome_flutter/font_awesome_flutter.dart";
+import "package:flutter_localized_locales/flutter_localized_locales.dart";
 
+import "package:inventree/api_form.dart";
 import "package:inventree/l10.dart";
+import "package:inventree/l10n/supported_locales.dart";
+import "package:inventree/main.dart";
 import "package:inventree/preferences.dart";
 
 
@@ -27,6 +31,8 @@ class _InvenTreeAppSettingsState extends State<InvenTreeAppSettingsWidget> {
   bool reportErrors = true;
   bool strictHttps = false;
 
+  Locale? locale;
+
   @override
   void initState() {
     super.initState();
@@ -46,14 +52,78 @@ class _InvenTreeAppSettingsState extends State<InvenTreeAppSettingsWidget> {
     reportErrors = await InvenTreeSettingsManager().getValue(INV_REPORT_ERRORS, true) as bool;
     strictHttps = await InvenTreeSettingsManager().getValue(INV_STRICT_HTTPS, false) as bool;
 
+    locale = await InvenTreeSettingsManager().getSelectedLocale();
+
     if (mounted) {
       setState(() {});
     }
   }
 
+  Future<void> _selectLocale(BuildContext context) async {
+
+    List<Map<String, dynamic>> options = [
+      {
+        "display_name": L10().languageDefault,
+        "value": null,
+      }
+    ];
+
+    // Construct a list of available locales
+    for (var locale in supported_locales) {
+      options.add({
+        "display_name": LocaleNames.of(context)!.nameOf(locale.toString()),
+        "value": locale.toString()
+      });
+    }
+
+    Map<String, dynamic> fields = {
+      "locale": {
+        "label": L10().language,
+        "type": "choice",
+        "choices": options,
+        "value": locale?.toString(),
+      }
+    };
+
+    launchApiForm(
+      context,
+      L10().languageSelect,
+      "",
+      fields,
+      icon: FontAwesomeIcons.checkCircle,
+      onSuccess: (Map<String, dynamic> data) async {
+
+        String locale_name = (data["locale"] ?? "") as String;
+        Locale? selected_locale;
+
+        for (var locale in supported_locales) {
+          if (locale.toString() == locale_name) {
+            selected_locale = locale;
+          }
+        }
+
+        await InvenTreeSettingsManager().setSelectedLocale(selected_locale);
+
+        setState(() {
+          locale = selected_locale;
+        });
+
+        // Refresh the entire app locale
+        InvenTreeApp.of(context)?.setLocale(locale);
+      }
+    );
+
+  }
+
   @override
   Widget build(BuildContext context) {
 
+    String languageName = L10().languageDefault;
+
+    if (locale != null) {
+      languageName = LocaleNames.of(context)!.nameOf(locale.toString()) ?? L10().languageDefault;
+    }
+
     return Scaffold(
       key: _settingsKey,
       appBar: AppBar(
@@ -142,6 +212,14 @@ class _InvenTreeAppSettingsState extends State<InvenTreeAppSettingsWidget> {
                 },
               ),
             ),
+            ListTile(
+              title: Text(L10().language),
+              subtitle: Text(languageName),
+              leading: FaIcon(FontAwesomeIcons.language),
+              onTap: () async {
+                _selectLocale(context);
+              },
+            ),
             ListTile(
               title: Text(L10().errorReportUpload),
               subtitle: Text(L10().errorReportUploadDetails),