Hello,There's quite a bit of information on translating Help content on the wiki: https://wiki.documentfoundation.org/UI_and_Help_files_Content_Guide
A TL;DR sort of summary or guideline on the XML tags part would be useful, so I'm asking if the following statement would be correct: "Do not translate anything inside a tag (that is, between angle brackets)."
Reading the wiki page, my understanding is that anything between < and the nearest > either should not be translated or has no effect if translated. The only exception to this would appear to be the xml-lang attribute in the <alt> tag. However, based on a quick search, the xml-lang attribute doesn't seem to be actually used in <alt> tags anywhere in Help. Perhaps the information on the wiki is outdated?