It sounds like we are on the same page then. If two separate plugins are made, I would request that my other suggestion gets included in the simpler plugin.
The simpler plugin could be called “Basic metadata match” and include “Basic Language Match” and “Title & Author Match”. The title & author match would just search for the book's title and author's last name, provided by what Calibre has set for each field, inside the book. After testing a few books it looks like it would work pretty well, the search will probably need to remove any subtitle in the title though.
The advanced plugin could be “Advanced Language Match”. The thing is that I'm not sure how useful this plugin would be for people using Calibre, and frankly how many would use it. If one wants to identify the language of a text, there are already tools for it, some here:
https://aclweb.org/aclwiki/Language_...fication_Tools along with Google translates automatic identification of a language. The ability to identify any language would be good to have in Calibre, but the basic plugin may end up being good enough anyway for 99% of people who use it.
So how about we start on the Basic metadata match plugin and decide which way to check for languages?