Translate "view cart" button and sentence

This can depend on your theme – what theme are you using?

Some words can not translate by using Popylang plugin. I faced with this issue at some part of my website also.

Im using noveau theme – https://themeforest.net/item/nouveau-multipurpose-retina-wordpress-theme/7510444.

If I can’t translate the button and sentence usng polylang plugin, how do I translate it then?

I suggest you buy the wpml plugin, you can translate everything with it. Otherwise you will get the perfect support for resolve every issue.