Hello,
Thanks for contacting Rank Math, and sorry for any inconvenience caused.
We have been trying to collaborate with Polylang for a few years but left the conversation when they refused to add the compatibility even though they have it for several other plugins (some of them have a smaller user-base compared to RM)
https://github.com/polylang/polylang/tree/master/integrations
You can check their public repository where we created a pull request (linked to from your opening post) a few years back and we would have maintained it (though that would not have happened ideally since we do not make changes in the plugin that breaks the compatibility).
Disappointingly, the compatibility needs to be added in their plugin as they added for other SEO plugins. We are more than committed to making that happen and always keep it updated, of course, if their team agreed and wanted to collaborate.
With that said, you can check the following page for alternatives that are 100% compatible with the Rank Math SEO plugin
https://rankmath.com/compatibility/
https://rankmath.com/compatibility/?s=Translate&post_type=rm_compatible
For the sitemap, if your categories are not getting added to the sitemap, please exclude the sitemaps from caching by following this guide:
https://rankmath.com/kb/exclude-sitemaps-from-caching/
Then, clear the website and browser cache and check the sitemap.
Hope that helps. Let us know if you need any other assistance.
Is there any other add-on you would recommend other than Polylang?
Hello,
I can recommend TranslatePress or Weglot which works perfectly well with Rank Math. You may refer to our compatibility page here: https://rankmath.com/compatibility/?s=translate&post_type=rm_compatible
Hope that helps and please do not hesitate to let us know if you need our assistance with anything else.
Hello,
Glad that helped.
Please feel free to reach out to us again in case you need any other assistance.
We are here to help.
Thank you.