There is only one file type that uses the .XLF extension:
XML formatted file based on the XLIFF (XML Localisation Interchange File Format) specification developed by the OASIS Technical Committee; used as a standard means of exchanging localizable data and related information in a lossless format.
Each XLIFF document contains one or more <file> elements. These elements identify the location of data sources, such as images, databases, properties files, etc.
Updated: November 6, 2018