I have created the German language file

[Mati1199]

{ "extensionName": { "message": "Anwendungsmenü" }, "description": { "message": "Eine WebExtension, die das Anwendungsmenü der Firefox-Titelleiste hinzufügt." },

"browserAction":    { "message":    "Firefox"   },

"popup_newTab": { "message":    "Neuer Tab" },
"popup_newWindow":  { "message":    "Neues Fenster" },
"popup_newPrivateWindow":   { "message":    "Neues privates Fenster"    },
"popup_openFile":   { "message":    "Datei öffnen…" },

"popup_edit":   { "message":    "Bearbeiten"    },
"popup_editCut":    { "message":    "Ausschneiden"  },
"popup_editCopy":   { "message":    "Kopieren"  },
"popup_editPaste":  { "message":    "Einfügen"  },
"popup_editUndo":   { "message":    "Rückgängig machen" },
"popup_editRedo":   { "message":    "Wiederherstellen"  },
"popup_editSelectAll":  { "message":    "Alles auswählen"   },
"popup_editDelete": { "message":    "Löschen"   },

"popup_findInPage": { "message":    "Seite durchsuchen…"    },
"popup_savePageAs": { "message":    "Seite sichern als…"    },
"popup_emailLink":  { "message":    "Link per Email senden…"    },

"popup_print":  { "message":    "Drucken…"  },
"popup_printPreview":   { "message":    "Druckvorschau" },
"popup_pageSetup":  { "message":    "Seite einrichten…" },

"popup_fullScreen": { "message":    "Vollbild"  },
"popup_sync":   { "message":    "Bei Sync anmelden" },
"popup_restart":    { "message":    "Neustart"  },
"popup_exit":   { "message":    "Beenden"   },

"popup_bookmarks":  { "message":    "Lesezeichen"   },
"popup_history":    { "message":    "Chronik"   },
"popup_downloads":  { "message":    "Downloads" },
"popup_addons": { "message":    "Add-ons"   },
"popup_options":    { "message":    "Optionen"  },
"popup_help":   { "message":    "Hilfe" },

"popup_dev":    { "message":    "Web-Entwickler"    },
"popup_devTools":   { "message":    "Werkzeuge ein-/ausblenden" },
"popup_devInspector":   { "message":    "Inspektor" },
"popup_devConsole": { "message":    "Web-Konsole"   },
"popup_devDebugger":    { "message":    "Debugger"  },
"popup_devStyleEditor": { "message":    "Stilbearbeitung"   },
"popup_devPerformance": { "message":    "Laufzeitanalyse"   },
"popup_devNetwork": { "message":    "Netzwerk"  },
"popup_devStorageInspector":    { "message":    "Speicher-Inspektor"    },
"popup_devDOM": { "message":    "DOM"   },
"popup_devToolbar": { "message":    "Entwickler-Symbolleiste"   },
"popup_devWebIDE":  { "message":    "WebIDE"    },
"popup_devBrowserToolbox":  { "message":    "Browser Toolbox"   },
"popup_devBrowserContentToolbox":   { "message":    "Browser Content Toolbox"   },
"popup_devBrowserConsole":  { "message":    "Browser-Konsole"   },
"popup_devResponsiveDesign":    { "message":    "Bildschirmgrößen testen"   },
"popup_devEyedropper":  { "message":    "Farbpipette"   },
"popup_devScratchpad":  { "message":    "JavaScript-Umgebung"   },
"popup_devServiceWorkers":  { "message":    "Service-Worker"    },
"popup_devConnect": { "message":    "Verbinden…"    },
"popup_devPageSource":  { "message":    "Seitenquelltext anzeigen"  },
"popup_devGetTools":    { "message":    "Weitere Tools laden"   },
"popup_workOffline":    { "message":    "Offline arbeiten " },

"popup_optionsToolbar_menu":    { "message":    "Symbolleisten" },
"popup_optionsToolbar_navigation":  { "message":    "Menüleiste"    },
"popup_optionsToolbar_bookmarks":   { "message":    "Lesezeichen-Symbolleiste"  },
"popup_optionsCustomize":   { "message":    "Anpassen…" },

"popup_helpFirefox":    { "message":    "Firefox-Hilfe" },
"popup_helpGettingStarted": { "message":    "Erste Schritte"    },
"popup_helpTour":   { "message":    "Tour durch Firefox"    },
"popup_helpShortcuts":  { "message":    "Tastenkombinationen"   },
"popup_helpHealthReport":   { "message":    "Firefox-Statusbericht" },
"popup_helpTroubleshootingInformation": { "message":    "Informationen zur Fehlerbehebung"  },
"popup_helpSubmitFeedback": { "message":    "Feedback senden…"  },
"popup_restartInSafeMode":  { "message":    "Mit deaktivierten Add-ons neu starten…"    },
"popup_helpAbout":  { "message":    "Über Firefox"  },

"options_header":   { "message":    "Optionen"  },
"options_theme":    { "message":    "Themes:"   },
"options_preferredWindowState": { "message":    "Bevorzugte Fenstergröße:"  },
"options_preferredWindowState_maximized":   { "message":    "Maximiert" },
"options_preferredWindowState_normal":  { "message":    "Normales Fenster"  }

}

[Mati1199]

Sorry, my English is not good and I can not cope with the website.