Rank Math recently published a workaround to make Polylang compatible with Rank Math by adding a compatibility code in the rank-math-ppl.php file. If you have not implemented this, you should – here’s the guide: https://rankmath.com/kb/polylang-compatibility/
If you have already added this compatibility code and are still not able to get it to work, you can try opening a ticket here with more information on the issue: https://support.rankmath.com/new-ticket/
First of all, you should review your Rank Math settings to make sure you have not misconfigured the plugin, i.e. via the Redirection module or Strip Category base options. If none of these are the culprits, you can try creating a ticket on support.rankmath.com with your website URL and maybe login details so they can help take a look for you.
It seems what you’ve encountered is the infamous ‘White Screen of Death’, which occurs when certain things go wrong with your WordPress installation. There are a number of reasons why this could happen, but the most common one is usually from your theme or plugin.
Since you’ve troubleshooted your plugins, why not try troubleshooting your themes also?
By simply renaming your current theme (which would make WordPress revert to a generic theme automatically)
