In case anyone runs into this issue:
Fixed it by hardcoding the relevant permalinks.
Auto generated ones are:
[(([^/]+/)*{wishlist-page-slug})(/(.*))?/page/([0-9]{1,})/?$] => index.php?pagename=$matches[1]&wishlist-action=$matches[4]&paged=$matches[5]
[(([^/]+/)*{wishlist-page-slug})(/(.*))?/?$] => index.php?pagename=$matches[1]&wishlist-action=$matches[4]
Just add your language ones with the lang prefix in functions.php as follows:
function YITH_polylang_rewrite_rules() {
//Lang 1
add_rewrite_rule('{lang1-slug}/(([^/]+/)*{wishlist-page-lang1-slug})(/(.*))?/page/([0-9]{1,})/?$','index.php?pagename=$matches[1]&wishlist-action=$matches[4]&paged=$matches[5]');
add_rewrite_rule('{lang1-slug}/(([^/]+/)*{wishlist-page-lang1-slug})(/(.*))?/?$','index.php?pagename=$matches[1]&wishlist-action=$matches[4]','top');
//Lang 2
add_rewrite_rule('{lang2-slug}/(([^/]+/)*{wishlist-page-lang2-slug})(/(.*))?/page/([0-9]{1,})/?$','index.php?pagename=$matches[1]&wishlist-action=$matches[4]&paged=$matches[5]');
add_rewrite_rule('{lang2-slug}/(([^/]+/)*{wishlist-page-lang2-slug})(/(.*))?/?$','index.php?pagename=$matches[1]&wishlist-action=$matches[4]','top');
// .... and so on
}
add_action('init', 'YITH_polylang_rewrite_rules', 10, 0);
Alex