If a work is specified to have multiple lyrics languages (for example, Aisling's Song), Picard doesn't save each of them to files using that work, but instead simply mul. I can somewhat understand this for the ID3v2.3 tags, where multiple values do seem to be allowed but with no guarantee offered for the text format, but not for v2.4 with its easy provision for multiple values. Even if this is a provision for other metadata formats that do only allow a single language, I feel it would make more sense to save the better data to those files that can support it.