Add localisable string for difficulty multiplier display

osu.Game/Localisation/DifficultyMultiplierDisplayStrings.cs

@@ -0,0 +1,19 @@
+// 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 DifficultyMultiplierDisplayStrings
+    {
+        private const string prefix = @"osu.Game.Resources.Localisation.DifficultyMultiplierDisplay";
+
+        /// <summary>
+        /// "Difficulty Multiplier"
+        /// </summary>
+        public static LocalisableString DifficultyMultiplier => new TranslatableString(getKey(@"difficulty_multiplier"), @"Difficulty Multiplier");
+
+        private static string getKey(string key) => $@"{prefix}:{key}";
+    }
+}