Updated: Comment #0
MatcherDumper::MAX_PARTS denotes the maximum number of parts a path can have in the new routing system.
This limitation is carried over from the old menu system. It is one, that we should try to avoid, though, if possible. In config_translation.module we have already hit the limit and need to work around it by providing multiple levels of pages all on one route. (Instead of
/.../translate/add/fr we have to do
/.../translate?action=add&langcode=fr and then dispatch to the appropriate forms ourselves by checking the request query.)
Currently MatcherDumper::MAX_PARTS is only used in one place in core and it can very easily be avoided.