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....
DLL (dynamic link library) files such as npctrl.dll are small programs, similar to EXE (executable) files, which allow multiple software programs to share the same functionality (eg. printing). For example, let's say you are running Windows and editing a document in Microsoft Word.