Hello, we are installing with UnifiedInstaller 5.1.1, and we have the following messages :
" Testing /usr/bin/python2.7 for Zope/Plone requirements....
/usr/bin/python2.7 looks OK. We will use it.
Unable to find libxml2 development libraries."
But in apt-get, libxml2 development appears installed in the last version.
"libxml2 is already the newest version (2.9.4+dfsg1-2.2+deb9u2).
libxml2-dbg is already the newest version (2.9.4+dfsg1-2.2+deb9u2).
libxml2-dev is already the newest version (2.9.4+dfsg1-2.2+deb9u2).
libxml2-doc is already the newest version (2.9.4+dfsg1-2.2+deb9u2).
libxml2-utils is already the newest version (2.9.4+dfsg1-2.2+deb9u2).
libxml2-utils-dbg is already the newest version (2.9.4+dfsg1-2.2+deb9u2).
"
that's the problem.
But this page says that if your have installed libxslt1-dev you should have xslt-config in /usr/bin so it's some mystery. Are you sure that libxslt1-dev installed correctly ?
well, install libxslt1-dev then it should not be that difficult under Debian, it's a one minute thing under Ubuntu. If you really can't install this library you should search help on a Debian forum, there is something wrong on your system.