Are you talking about this in back end featured image or front end. If it is for back end then you may ask for the polylang plugin developer support. If it is for front end then you need to type that language (you language) in title and editor.) What ever language you type there will be displayed in that language.
Yes in slogan you can change it but you must type your language.
We are not much familiar with polylang plugin so you may ask polylang plugin developer for more information.
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