Add tooltips showing current connecting status

osu.Game/Localisation/ToolbarStrings.cs

@@ -0,0 +1,24 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Localisation;
+
+namespace osu.Game.Localisation
+{
+    public static class ToolbarStrings
+    {
+        private const string prefix = @"osu.Game.Resources.Localisation.Toolbar";
+
+        /// <summary>
+        /// "Connection interrupted, will try to reconnect..."
+        /// </summary>
+        public static LocalisableString ConnectionInterruptedWillTryTo => new TranslatableString(getKey(@"connection_interrupted_will_try_to"), @"Connection interrupted, will try to reconnect...");
+
+        /// <summary>
+        /// "Connecting..."
+        /// </summary>
+        public static LocalisableString Connecting => new TranslatableString(getKey(@"connecting"), @"Connecting...");
+
+        private static string getKey(string key) => $@"{prefix}:{key}";
+    }
+}

osu.Game/Overlays/Toolbar/ToolbarUserButton.cs

@@ -102,12 +102,18 @@ namespace osu.Game.Overlays.Toolbar
             switch (state.NewValue)
             {
                 case APIState.Connecting:
+                    TooltipText = ToolbarStrings.Connecting;
+                    spinner.Show();
+                    break;
+
                 case APIState.Failing:
+                    TooltipText = ToolbarStrings.ConnectionInterruptedWillTryTo;
                     spinner.Show();
                     break;
 
                 case APIState.Offline:
                 case APIState.Online:
+                    TooltipText = string.Empty;
                     spinner.Hide();
                     break;