Improved SafeFileName method to include all valid characters as listed by RFC 3986 section 2.2 Reserved Characters (January 2005) and character data chars that could be ambiguous

Now characters like Chinese characters are allowed in the filenames, which addresses the issue below
#U4-885 Fixed

src/Umbraco.Core/IO/IOHelper.cs

@@ -209,7 +209,37 @@ namespace Umbraco.Core.IO
         /// <returns>A safe filename without any path specific chars.</returns>
         internal static string SafeFileName(string filePath)
         {
-            return !String.IsNullOrEmpty(filePath) ? Regex.Replace(filePath, @"[^a-zA-Z0-9\-\.\/\:]{1}", "_") : String.Empty;
+            if (String.IsNullOrEmpty(filePath))
+                return String.Empty;
+
+            if (!String.IsNullOrWhiteSpace(filePath))
+            {
+                foreach (var character in Path.GetInvalidFileNameChars())
+                {
+                    filePath = filePath.Replace(character, '_');
+                }
+            }
+            else
+            {
+                filePath = String.Empty;
+            }
+
+            // Adapted from: http://stackoverflow.com/a/4827510/5018
+            // Combined both Reserved Characters and Character Data 
+            // from http://en.wikipedia.org/wiki/Percent-encoding
+            var stringBuilder = new StringBuilder();
+
+            const string reservedCharacters = "!*'();:@&=+$,/?%#[]-~{}\"<>\\^`| ";
+
+            foreach (var character in filePath)
+            {
+                if (reservedCharacters.IndexOf(character) == -1)
+                    stringBuilder.Append(character);
+                else
+                    stringBuilder.Append("_");
+            }
+
+            return stringBuilder.ToString();
         }
     }
 }