First off let me say that I am flabbergasted that this has been sitting here, unanswered for over a month. I am so sorry about that. I was not notified because it was not set to a support topic. I will look into the matter and get it corrected so this does not happen again.
To answer your question, yes would be able to add this. Please see this https://codex.wordpress.org/Function_Reference/add_post_meta. Here is another to help you understand more https://torquemag.io/2017/10/customize-post-metadata/ as well as one more http://webcraft.tools/displaying-custom-post-meta/
I don’t think it’s necessary to add a language meta as you can add this to your site with a plugin. The user can select what language they want to use and then your entire site will be translated into that language for them.
The type on the other hand can be added but it would take some doing to accomplish it. As you can see from the articles I linked to, it can take some doing.
Have you thought about maybe using tags