I resume this quite old topic because, in the meantime, I came across the
Google Takeout service, that allows to download hangouts histories.
The download is a zip archive containing an html and a json files. The json is very verbose, but I think that it would be easy for developers to create a parser that allows to import the histories into Miranda database. Is there any chance for that?
There is even an
online php parser (code is available
here) that allows to read and download the histories in various formats.
An "hangouts import" plugin, that allows to import the histories retrieved from Google Takeout will solve my problem to have almost unreadable histories for my hangouts conversations.