Hello!
The reason this won’t work is that WordPress isn’t made for multilingual setups. WordPress’ Post Meta API only allows us to store simple information tied to a post ID–we can’t pre-assign languages to this data for translation plugins to pick up. This also accounts for the site options. This is why Yoast SEO didn’t work for you, either.
I’m afraid the translation plugins must provide workarounds for us–without us having to interfere or contribute. Otherwise, over 30,000 plugins and developers must yield to a single non-standard solution.
For example, WPML lets us specify the metadata that can be translated, and Polylang enables you to bind separate posts together with each their own language. It’d be helpful to reach out to BestWebSoft to see what the best workaround is. We’re also open to discussing solutions with BestWebSoft, may they want to reach out to us.
As a side note, to get the best results, you’d want to maintain multiple sites, with each their own language. This way, you can tailor each site to a language (which is often bound to a culture). This is how WordPress.org and WordPress.com do it, via WordPress Multisite. Via the hreflang link relationship attribute, the sites point to each other.
I hope this explains the situation. I hope you’ll find an applicable workaround soon. Cheers!
