Japanese translation added

src/MpvNet.Windows/WPF/WpfTranslator.cs

@@ -13,6 +13,7 @@ public class WpfTranslator : ITranslator
         new("english", "en", "en"),
         new("chinese-china", "zh-CN", "zh"),  // Chinese (Simplified)
         new("german", "de", "de"),
+        new("japanese", "ja", "ja"),
     };
 
     public string Gettext(string msgId)

src/MpvNet.Windows/WinForms/MainForm.cs

@@ -392,7 +392,7 @@ public partial class MainForm : Form
             }
 
             recentMenuItem.Items.Add(new WpfControls.Separator());
-            var clearMenuItem = new WpfControls.MenuItem() { Header = "Clear List" };
+            var clearMenuItem = new WpfControls.MenuItem() { Header = _("Clear List") };
             clearMenuItem.Click += (sender, args) => App.Settings.RecentFiles.Clear();
             recentMenuItem.Items.Add(clearMenuItem);
         }