Hi, the language in your news sitemap corresponds with the language set on your post.
If you are writing posts in Hindi, then you should set your WordPress site language to Hindi. If you do not do that, then posts will get marked as en_US, not only in the news sitemap but also in the page source code.
Search engines will get confused if the language marker in the source code does not match the language used on your page/post. It will cost you traffic.
If you are writing in multiple languages, you should install a multi-language plugin like Polylang. It will allow you to mark certain posts as one language and other posts as another language. This will take care of the correct language marker in both source code and in the news sitemap.
Note: you can always set you admin language to English if you wish, while still keeping the site (front-end) language in Hindi.
