How to set up switching between Bitrix sites while saving the current page?

Question

1C-Bitrix

Task:
the site in Russian is in the root /
the site in English is in the folder /en/
URLs are all identical, the only difference is this.
How to correctly set a link or a condition for switching between language versions, while saving the current page? As I understand it, we need to dig in the direction of use <?=$APPLICATION->GetCurPage(); ?>
. But how exactly to prescribe the condition?

Answer 1

Look towards $APPLICATION->GetCurPageParam