Having Russian and English pages division makes sense for readers.
But I think you should just have one single sitemap for your whole site. The sitemap plugin will find all pages and list them in sitemap.xml file. And then crawlers will find that sitemap and go through all the pages. The grouping and order doesn’t matter.
I wouldn’t bother splitting multiple sitemaps. Only worthwhile if you hit a limit I think like 50MB or 50 000 items per sitemap. Then it you have to split your sitemap (whether by arbitrary or logical grouping) so Google sees it as valid. But unless you are Pinterest or Instragram I don’t think you will have that many pages.
Can you share a repo link so I can reproduce locally?
The sitemap plugin gets site.collections to handle posts (posts is a kind of collection), so you need to figure out what happens if you just do this - I would expect both RU and EN posts would be there if the posts are getting rendered as HTML pages for users to see.
When running Jekyll serve/build I noticed it builds your site twice.
Building site for language: "ru" to: /Users/mcurrin/public_repos/cmsminers/_site/ru
...
Building site for language: "en" to: /Users/mcurrin/public_repos/cmsminers/_site/en
Putting sitemaps aside for a moment, it looks building the site twice is weird.
What I would expected is one site, with one index.html and one sitemap.xml generated at the root which has all the pages in it (as in my earlier comment).
And then language/specific files in dirs.
e.g.
en/
blog/
...
index.html # English home
ru/
blog/
...
index.html # Russian home
index.html # Website home
sitemap.xml
Maybe the two-site way is the way the internationalization plugin is meant to work, or it needs more configuration on your part?
It’s complicated to follow your project because of NPM + a bunch of plugins + Minimal Mistake needing massive config + internationalization + sitemap plugin + your own robots and sitemap files + an unusually high number of layouts and include files.
Whoever comes here from google, this code regularly generates a sitemap for Jekyll Multiple Languages and allows you to exclude pages you don’t need: