A sample <file> element of 4D internal XLIFF files looks like this:
<file datatype="x-STR#" original="undefined" source-language="en-US" target-language="en-US" product-version="v11">
Based on the Oasis open documentation on XLIFF files the required attributes for the file element are original, source-language, and datatype. That documentation can be found at the following link:
4D does load XLIFF files without those necessary attributes though. Only the target-language attribute must be included, otherwise no text is inserted.