Adding string translation custom function

I want to translate a custom function that adds “Log in/out” menu items for Woocommerce.
The problem is that I am not sure what is the correct way to register the strings.

This is the function

add_filter( 'wp_nav_menu_items', 'add_loginout_link', 10, 2 );

function add_loginout_link( $items, $args ) {

   if (is_user_logged_in() && $args->theme_location == 'grve_top_right_nav') {

       $items .= '<li><a href="'. wp_logout_url( get_permalink( woocommerce_get_page_id( 'myaccount' ) ) ) .'">Log Out</a></li>';

   }

   elseif (!is_user_logged_in() && $args->theme_location == 'primary') {

       $items .= '<li><a href="' . get_permalink( woocommerce_get_page_id( 'myaccount' ) ) . '">Log In</a></li>';

   }

   return $items;

}

In my case, I need to translate the words “log out” and “log in”

I understand that I have to use pll_register_string in my functions.php but not sure how to use.

Any help would be much appreciated, thanks!