[22838], [23570], [23573]: Bug 635240 RFE: Rename translations in gnucash-docs from <LANG>_<region> to <LANG>

Backport changes to windows build script

22838: Temporarly disable ja guide html help ...
23570: Change guide and help translation directories To match gnucash-docs … 
23573: there was still one "_JP" although currently commented out 

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/branches/2.4@23625 57a11ea4-9604-0410-9ed3-97b8803252fd