Hello,
To add languages to the header next to the menu use Widgets element https://prnt.sc/1tg32en and choose the widget area you want to display. In the Appearance > Widgets > Left side top bar area > add the language switcher widget.
As I know Polylang won’t offer multiple currency options but it would be better for your to clarify that from the plugin author. If they don’t have such option then you will need an additional plugin to get multicurrency on your site.
Edit Cross-sell products and change border-color according to your needs in the Single product builder settings https://prnt.sc/1tg3wc7
Regards