IMHO it would be best if bison.texi (and all other GNU manuals written in English) did not read txi-en.tex in the first place. Removing the "@documentlanguage en" line is all that is needed, and since US English is the default for TeX and Texinfo and always will be, there are no ill effects.
I'm not enthused about syncing ~20 new files (which hardly ever change) into gnulib. Also, for perfect synchronicity, that would imply uploading and maintaining those txi-??.tex files also on ftp.gnu.org. Yuck. -k P.S. Independent of that, I suggest removing the @setchapternewpage odd from bison.texi. Blank pages are just a nuisance for everything except bound books. In the event that the FSF reprints the bison manual on paper, they are perfectly capable of specifying that in their final print run.