[Resolved] Gravity Forms: Confirmation redirection in other language than default language doesn't use the url...

add_filter('login_url', 'my_login_page', 10, 3);
function my_login_page($login_url, $redirect, $force_reauth) {

    // 1) Pull redirect_to from CURRENT REQUEST (most important when you're on the login page)
    $request_redirect = '';
    if (isset($_GET['redirect_to']) && $_GET['redirect_to'] !== '') {
        // wp_unslash because WP may add slashes in some contexts
        $request_redirect = wp_unslash($_GET['redirect_to']);
    }

    // 2) Pull redirect_to already present in $login_url (sometimes WP already embedded it)
    $existing_redirect = '';
    $login_parts = wp_parse_url($login_url);
    if (!empty($login_parts['query'])) {
        parse_str($login_parts['query'], $q);
        if (!empty($q['redirect_to'])) {
            $existing_redirect = $q['redirect_to'];
        }
    }

    // 3) Decide final target (priority: current request > $redirect > existing in login_url)
    $target = $request_redirect ?: ($redirect ?: $existing_redirect);

    // 4) Decide language based on TARGET path (or fallback to current request URI)
    $target_path = '';
    if (!empty($target)) {
        $tp = wp_parse_url($target);
        $target_path = $tp['path'] ?? '';
    } else {
        $target_path = wp_parse_url($_SERVER['REQUEST_URI'] ?? '')['path'] ?? '';
    }

    $is_en = (strpos($target_path, '/en/') === 0)
        || (strpos($_SERVER['REQUEST_URI'] ?? '', '/en/') === 0);

    $base = $is_en ? home_url('/en/login-registration/') : home_url('/login/');

    // 5) Loop prevention: only suppress redirect_to if the target is *exactly* the login page.
    // IMPORTANT: do NOT trigger this if the user provided redirect_to in the current request.
    if (empty($request_redirect) && !empty($target_path)) {
        if ($is_en && strpos($target_path, '/en/login-registration/') === 0) {
            return $base;
        }
        if (!$is_en && strpos($target_path, '/login/') === 0) {
            return $base;
        }
    }

    // 6) Build final URL with exactly one redirect_to
    if (!empty($target)) {
        $base = add_query_arg('redirect_to', $target, $base);
    }
    if ($force_reauth) {
        $base = add_query_arg('reauth', '1', $base);
    }

    return $base;
}