Fix startup localization issues

Flow.Launcher.Core/Plugin/PluginManager.cs

@@ -1,4 +1,4 @@
-using Flow.Launcher.Core.ExternalPlugins;
+using Flow.Launcher.Core.ExternalPlugins;
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
@@ -308,7 +308,8 @@ public static PluginPair GetPluginForId(string id)
 
         public static IEnumerable<PluginPair> GetPluginsForInterface<T>() where T : IFeatures
         {
-            return AllPlugins.Where(p => p.Plugin is T);
+            // Handle scenario where this is called before all plugins are instantiated, e.g. language change on startup
+            return AllPlugins?.Where(p => p.Plugin is T) ?? Array.Empty<PluginPair>();
         }
 
         public static List<Result> GetContextMenusForPlugin(Result result)

Flow.Launcher.Core/Resource/Internationalization.cs

@@ -58,6 +58,9 @@ internal void AddPluginLanguageDirectories(IEnumerable<PluginPair> plugins)
 
         private void LoadDefaultLanguage()
         {
+            // Removes language files loaded before any plugins were loaded.
+            // Prevents the language Flow started in from overwriting English if the user switches back to English
+            RemoveOldLanguageFiles();
             LoadLanguage(AvailableLanguages.English);
             _oldResources.Clear();
         }