Try this,
$select = db_select('Your table name', 's');
$select = $select->fields('s',array('languages_name','id'));
// 'languages_name' , 'id' this is a column
$queried_nodes = $select->execute()
->fetchAllAssoc('id');
$lang_list = array();
foreach ($queried_nodes as $result)
{
$lang_list[$result->languages_name] = t($result->languages_name);
}
after set a $lang_list variable
$form['user_list']=array(
'#type'=>'select',
'#title' => t('Language'),
'#options' => $lang_list,//array of language
'#multiple' => false,
'#attributes'=>array('size'=>4),
'#weight'=>8,
);
you are create a new Language table or content types and you use a drupal inbuilt language list so try this code.
include_once DRUPAL_ROOT . '/includes/iso.inc';
$lang = _locale_get_predefined_list();
$lang_list = array();
foreach ($lang as $key => $value)
{
$lang_list[$value[0]] = t($value[0]);
}
after use a $lang_list
varible in form api