Flat rate is common in broadband access to the Internet in the USA and many other countries. A charge tariff is a class of linear rate, different from the flat rate, where the user is charged by the uploads and downloads (data transfers).
MUI stands for Multilingual User Interface and .dll.mui files are simply libraries(Dlls) that contain resources dedicated to localization : for an application to support multiple languages,dlls containing specific resources must be available eg language resources(arabic,french,english,chinese....
Files that contain the .dl_ file extension contain a backup copy of a Microsoft Windows dynamic link library (DLL) file. A dynamic link library is the file format that Microsoft uses for shared library purposes.LL files are similar in nature to EXE files. DLL files can be compressed in order to make it easier for a user to download the file or to save space on a user's hard drive. Compression is usually performed when a backup copy of a DLL file is made.