perf: update translate with lang switched

STranslate/MainWindow.xaml

@@ -102,6 +102,7 @@
                 <ComboBox x:Name="InCombo"
                           Style="{DynamicResource cmbstyle}"
                           ItemsSource="{Binding InputCombo}"
+                          SelectionChanged="SelectionChanged"
                           SelectedItem="{Binding InputComboSelected,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" />
                 <Separator Margin="20,0"/>
                 <TextBlock Text="目标语言:  "
@@ -109,6 +110,7 @@
                 <ComboBox x:Name="OutCombo"
                           Style="{DynamicResource cmbstyle}"
                           ItemsSource="{Binding OutputCombo}"
+                          SelectionChanged="SelectionChanged"
                           SelectedItem="{Binding OutputComboSelected,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" />
             </StackPanel>
             

STranslate/MainWindow.xaml.cs

@@ -301,5 +301,14 @@ namespace STranslate
         private bool _IsTopmost { get; set; }
         private readonly string _TopmostTemplateName = "ButtonTemplateTopmost";
         private readonly string _UnTopmostTemplateName = "ButtonTemplateUnTopmost";
+
+        private void SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
+        {
+            if (!string.IsNullOrEmpty(vm?.InputTxt))
+            {
+                vm.IdentifyLanguage = string.Empty;
+                _ = vm?.Translate();
+            }
+        }
     }
 }