Language setting should apply to *ALL* nodes (i.e. site-wide)

FYI: I have:

1. enabled following modules 'Locale' & 'Content translation' ONLY (i.e. just optional core modules and no other modules),
2. set 'Language negotiation' (admin/settings/language/configure) to value "Path prefix only.",
3. added one non default language (admin/settings/language),
4. set 'Multilingual support' (admin/content/node-type/{content_type}) to value "Enabled, with translation" and
5. enabled the 'Language switcher' block (admin/build/block).

The behavior described in the start post occurs also with the standard 'language switcher' block (i.e. without a dropdown field).
So, the root cause of this issue is likely after line 556 of the file 'locale.module' (part of the core module 'Locale'):

// ---------------------------------------------------------------------------------
// Language switcher block

/**
 * Implementation of hook_block().
 * Displays a language switcher. Translation links may be provided by other modules.
 */
function locale_block($op = 'list', $delta = 0) {
  if ($op == 'list') {
    $block[0]['info'] = t('Language switcher');
    // Not worth caching.
    $block[0]['cache'] = BLOCK_NO_CACHE;
    return $block;
  }

  // Only show if we have at least two languages and language dependent
  // web addresses, so we can actually link to other language versions.
  elseif ($op == 'view' && variable_get('language_count', 1) > 1 && variable_get('language_negotiation', LANGUAGE_NEGOTIATION_NONE) != LANGUAGE_NEGOTIATION_NONE) {
    $path = drupal_is_front_page() ? '<front>' : $_GET['q'];
    $languages = language_list('enabled');
    $links = array();
    foreach ($languages[1] as $language) {
      $links[$language->language] = array(
        'href'       => $path,
        'title'      => $language->native,
        'language'   => $language,
        'attributes' => array('class' => 'language-link'),
      );
    }

    // Allow modules to provide translations for specific links.
    // A translation link may need to point to a different path or use
    // a translated link text before going through l(), which will just
    // handle the path aliases.
    drupal_alter('translation_link', $links, $path);

    $block['subject'] = t('Languages');
    $block['content'] = theme('links', $links, array());
    return $block;
  }
}