You can add either single link or organize multiple links into dropdown menus.

Adding links:

1- Go to 'Site administration' then 'Appearance' section, scroll down to 'Advanced Theme settings' and click on it.

2-  Scroll down the 'Custom menu items'.

To add external link:

Google|https://www.google.com

To add internal link:

About US|/mod/page/view.php?id=110

To enable link translations based on the chosen language:

About US|/mod/page/view.php?id=110||en
من نحن|/mod/page/view.php?id=110||ar
À Propos de Nous|/mod/page/view.php?id=110||fr

To add external links dropdown:

External Links|||
-Google|https://www.google.com
-Yahoo|https://www.yahoo.com

To add internal links dropdown: 

Internal Links|||
-All Courses|/mod/page/view.php?id=100
-All Categories|/mod/page/view.php?id=101

To enable links dropdown translations based on the chosen language:

Internal Links|||en
-All Courses|/mod/page/view.php?id=100||en
-All Categories|/mod/page/view.php?id=101||en
الراوبط الداخلية|||ar
-جميع المساقات|/mod/page/view.php?id=100||ar
-جميع التصنيفات|/mod/page/view.php?id=101||ar
liens internes||fr
-Tous les Cours|/mod/page/view.php?id=100||fr
-Toutes les Catégories|/mod/page/view.php?id=101||fr