How to display tabbed menu, created via hook_menu?
Alright, I found the problem: my tabs definitions were lacking the extra line

'access callback' =&gt; TRUE,


With this line in each tab definition, the tabs show up as extected.
Here is my final code for dummy_module.module:

&lt;?php

/**
 * Implements hook_menu().
 */
function dummy_module_menu() {
  $items = array();
  $items['dummy_module'] = array(
    'title' =&gt; 'dummy_module',
    'page callback' =&gt; 'temp_output',
    'access callback' =&gt; TRUE,
    'weight' =&gt; 30
  );
  $items['dummy_module/new_tab1'] = array(
    'title' =&gt; 'Current 1',
    'type' =&gt; MENU_DEFAULT_LOCAL_TASK,
    'page callback' =&gt; 'temp_output1',
    'access callback' =&gt; TRUE,
    'weight' =&gt; 1
  );
  $items['dummy_module/new_tab2'] = array(
    'title' =&gt; 'Current 2',
    'type' =&gt; MENU_LOCAL_TASK,
    'page callback' =&gt; 'temp_output2',
    'access callback' =&gt; TRUE,
    'weight' =&gt; 2
  );

  return $items;
}


function temp_output() {
  return 'Hello world!';
}


function temp_output1() {
  return 'Hello world 1!';
}

function temp_output2() {
  return 'Hello world 2!';
}