Why are no topics/ posts displayed at my homepage?
You need to set read permissions as global forum moderator: Open the edit mode under the categories tab and select one of your subcategories. Set read and write permissions for user levels and so on and save your settings. If you want, activate "Allow guests to read" to make your selected subcategory public.
How can I translate my forum?
You need to translate phrases in the SocialEngine translation tool (ids are starting at 18001000) and in the forum translation file. The translation file can be found in your "/locale" directory, e.g. "/locale/forum.en.php". Simply copy that file and rename it to "forum.YOUR_LANGUAGE_CODE.php" and translate the phrases in that file (always the second line). If you are using SocialEngine version 2 you also need to modify the "language map array" in "/header_forum.php".