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....
March 31, 2015. DLL files are used in conjunction with other programs as valuable resource files, but they can be opened independently for customization. Additionally, other executable formats, like EXE or ActiveX Controls, can be opened for individualized viewing.