EPUB2 can't satisfy package language requirement

With 1.2.7, it looks like it's now impossible to create an EPUB2 file that can satisfy both ace and epubcheck.

1.2.7 raises an issue if language isn't declared in the package declaration (see #371).

But epubcheck doesn't allow this in EPUB2. If I try to include xml:lang in the package declaration of an EPUB2 file, epubcheck raises an error:

`ERROR(RSC-005): File.epub/OEBPS/content.opf(1,102): Error while parsing file: attribute "xml:lang" not allowed here; expected attribute "id", "unique-identifier" or "version"`

Should the language requirement only apply to EPUB3?