Well now that you say so, that statement is so! I think that missing documentation is available from plone.org/documentation/ for versions Plone 3, which is still valid for Plone versions 4 and 5.
Even necessary documentation on how to implement i18n javascript, for example, i18n for Angular.js applications clients with Plone as backend, for now I'm trying to understand the operation of the library jarn.jsi18n.
That time had not seen the article written by this company, I remember that I was very useful for Plone 2.5 and 3 versions. I'm sure this article can be very inspiring for good content structure, more practical.
Something I like about this article is that it describes common problem-solving cases such as the @mauritsvanrees article