feat: Translate frontend/src/i18n/en.json in de

95% of minimum 50% translated source file: 'frontend/src/i18n/en.json'
on 'de'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

frontend/src/i18n/de.json

@@ -13,7 +13,7 @@
     "download": "Herunterladen",
     "file": "Datei",
     "folder": "Ordner",
-    "fullScreen": "Toggle full screen",
+    "fullScreen": "Vollbildmodus umschalten",
     "hideDotfiles": "Versteckte Dateien ausblenden",
     "info": "Info",
     "more": "mehr",
@@ -24,7 +24,7 @@
     "ok": "OK",
     "permalink": "permanenten Verweis anzeigen",
     "previous": "vorherige",
-    "preview": "Preview",
+    "preview": "Vorschau",
     "publish": "Veröffentlichen",
     "rename": "umbenennen",
     "replace": "Ersetzen",