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Choose the menu item Plugins->Manage plugins and click on the button Upload Plugin. Choose the zip file you've downloaded in the Smartstore Community Marketplace and click on Upload & Install. The plugin has now been installed and can be configured in the plugin management area.
Themes
Choose the menu item Configuration>Themes and click on the button Upload Theme. Choose the zip file you've downloaded in the Smartstore Community Marketplace and click on Upload & Install. The theme has now been installed and can be configured in the theme management area.
Language packs
Choose the menu item Configuration->Regional Settings->Languages. If you haven't yet created the language you want to import, create it by clicking on the button New and visiting the details view of this language. Here, you need to click on the button Import Resources. Choose the xml file you've downloaded in the Smartstore Community Marketplace and click on Import Resources. The language can now be chosen within your shop by your customers as long as it has already been activated.