If your site needs to be multi-language, first you need to add the languages under Optionen > Languages. Similarly if your site needs to be just one language you can limit it here. In the Wert field enter your desired languages comma separated and in short from, for example "de,en,fr". Now when you enter your Feature content, you can switch between languages using the Inhaltssprache nav on the top right. If you only enter one language the nav is not displayed.
Now you can control which language should be displayed in the frontend by using the $currentlang variable. For example you could build this into your navigation paths. In the standard ZMS checkout the variable is set under the "Data fetching" section of the page header.
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# Data fetching #
#################
$pages = $PAGEOBJ->GetPages('nav_display=1 AND admin='n'');
$navmeta = $NAVIGATIONOBJ->GetMetaData();
$currentlang = $GLOBALS['LANGUAGEOBJ']->GetLanguage();