Ok... I found a solution on StackOverflow: https://stackoverflow.com/questions/41846364/ordering-categories-alphabetically-in-prestashop-top-menu
we need to override the ps_mainmenu with this content:
use PrestaShop\PrestaShop\Core\Module\WidgetInterface;
class Ps_MainMenuOverride extends Ps_MainMenu implements WidgetInterface
{
protected function generateCategoriesMenu($categories, $is_children = 0)
{
$categories = $this->sortCategories($categories);
return parent::generateCategoriesMenu($categories, $is_children);
}
public function sortCategories($categories)
{
uasort($categories, 'cmpcat');
foreach($categories as $k => $category)
{
if (isset($category['children']) && !empty($category['children'])) {
$children = $this->sortCategories($category['children']);
$categories[$k]['children'] = $children;
}
}
return $categories;
}
}
function cmpcat($a, $b) {
return strcmp($a['name'], $b['name']);
}