Thanks pigeonflight.
I saw "Ubuntu 16.04: Zope instance terminated by SIGSEGV (core dumped)" and worked through it. But I could not see a real solution. I did what jensens proposed in the last post, but my Python (Python 2.7.12) seems newer.
I think the problem looks the same but may be caused by the three errors indicated:
Error while compiling /opt/plone/buildout-cache/eggs/python_gettext-3.0-py2.7.egg/pythongettext/tests/test5.po
Error while compiling /opt/plone/buildout-cache/eggs/python_gettext-3.0-py2.7.egg/pythongettext/tests/test_escape.poandchmod: changing permissions of '/opt/plone/zinstance/bin/buildout': Operation not permitted`