Locale module and language prefix in url

Question

I had been working on module and well aware of hook_menu for passing url arguments to call back. For instance:

$items['webtv/block/%/playlist/edit/%'] = array(
    ...
    'page callback' => 'drupal_get_form',
    'page arguments' => array('webtv_playlist_form', 5, 2),
    ...
);

and callback as

function webtv_playlist_form($form_state, $fifth_arg, $second_arg){
...
}

Beside that arg() function is another utility to get url arguments by their positions.

$second_arg = arg(2);
$fifth_arg = arg(5);

When I enable locale module to make web as multilingual, URLs are classified with prefix as language symbol. Example:

en/webtv/block/%/playlist/edit/%

OR

nl/webtv/block/%/playlist/edit/%

This thing displaces the logical placement of arguments to right, now the correct placement of arguments (according to example) is:

$second_arg = arg(3);
$fifth_arg = arg(6);

How to set-up module independent of such argument placement issues?

Answer 1

Looking at Drupal core code (in example, node_menu()), menu callback using menu placeholders are not adjusted to work when locale.module is enabled, nor local.module alters the menus defined from other modules. In fact, language_initialize(), called on Drupal bootstrap contains the following code:

case LANGUAGE_NEGOTIATION_PATH_DEFAULT:
case LANGUAGE_NEGOTIATION_PATH:
  // $_GET['q'] might not be available at this time, because
  // path initialization runs after the language bootstrap phase.
  $args = isset($_GET['q']) ? explode('/', $_GET['q']) : array();
  $prefix = array_shift($args);
  // Search prefix within enabled languages.
  foreach ($languages as $language) {
    if (!empty($language->prefix) && $language->prefix == $prefix) {
      // Rebuild $GET['q'] with the language removed.
      $_GET['q'] = implode('/', $args);
      return $language;
    }
  }

The code is removing the language ID passed in the URL. If locale.module is correctly set, the menu callback definitions should not be changed when the module is enabled.