This repository contains the sources of the OTRS admin manual. They are located in en/ and stored in docbook format. The other languages are automatically generated with the help of po4a and the translation files in i18n.
You need to install the xsltproc and docbook-xsl packages (names may vary depending on your distribution).
Then you can run
cd /tmp
xsltproc --xinclude /usr/share/xsl/docbook-xsl/html/chunk.xsl /path/to/doc-admin/en/book.xml
The paths may vary, on MacOS docbook-xsl is located in /opt/local/xsl/...
You need to install the xmllint and docbook-xml packages.
Then you can run
xmllint --postvalid --nonet --xinclude --noout /path/to/doc-admin/en/book.xml
You will see some errors like
content/administration/ticket/states.xml:154: element link: validity error : IDREF attribute linkend references an unknown ID "Ticket:Frontend::Agent::Ticket::ViewEmailNew:Ticket::Frontend::AgentTicketEmail_StateDefault"
These are not problematic as a part of the admin manual is autogenerated - the configuration parameter reference. If you only see these link validity errors everything should be fine.
Please refer to http://doc.otrs.org/developer/stable/en/html/translating-docs.html.