Bulk redirect in WP multilang using .htaccess?

Question

Search Engine Optimization

Actually the essence of the issue. There is a site on WP in 4 languages ​​with 15k pages. A redesign was made with a change in the structure of the site. The customer is insanely afraid of losing positions (yes, I know that there will be a drawdown in positions anyway), so it was decided to set up a redirect map via .htaccess. Doing a redirect at the category level will not work, because part of the pages will be transferred to their counterpart, the rest will go to the category. How to do it all right? First, register a redirect within the framework of languages ​​and then for each url of the form:
/oldurl /newurl
Or immediately insert language versions into the redirect:
site.com/en/category/page1 site.com/en/page1
site.com/ru/category/ page1 site.com/en/page1
site.com/de/category/page1 site.com/de/page1