Now I have changed the Settings.yaml (see below). Backend Login: Page Not Found .. but when I add @user-admin to the url (it works). TYPO3: TYPO3CR: contentDimensions: 'language': label: 'Language' icon: 'icon-language' default: 'de' defaultPreset: 'de' presets: 'de': label: 'Deutsch' values: ['de'] uriSegment: 'de'