there appears to be considerable information about this file--some says it's part of your system--some says it's 'possibly' malware.
it's been on my system since 30 days after I installed the OS in 2010 with no apparent problems.
"MUI" extension is for Language Specific Resource File(s);
"A language-specific resource file normally contains user interface strings and other elements that require localization for a particular language. Your MUI application uses one language-specific resource file per supported language. The LN file for the application is the same for each language-specific resource file."
Nothing to be concerned about unless you are experiencing some problems and suspect an infection. Use a respected AV program to run a scan if you have doubts about the files integrity.
HTH
My Computer
At a glance
Windows 7 Professional x64Intel i5 quad processor16 GBRadeon HD 5770