MAINT: add i18n translation files

locales/de/translation.json

+{
+  "Login": "Anmelden",
+  "Authentication failed": {
+    " Username or password wrong": "Anmeldung fehlgeschlagen. Username oder passwort falsch."
+  },
+  "Username": "Username",
+  "Insert your username": "Username eintragen.",
+  "Password": "Passwort",
+  "Insert your password": "Passwort eintragen.",
+  "Click to log in": "Klicken zum Anmelden.",
+  "Show login form": "Zeige das Anmeldeformular.",
+  "Please log in!": "Bitte anmelden!",
+  "Open user menu": "Öffne Usermenu für {{session_info.username}}",
+  "Logout": "Abmelden",
+  "Click to log out": "Klicken zum Abmelden.",
+  "You have been logged out": "Abgemeldet.",
+  "Logout failed": "Fehler beim Abmelden"
+}

locales/en/translation.json

+{
+  "Login": "Login",
+  "Authentication failed": {
+    " Username or password wrong": "Authentication failed. Username or password wrong."
+  },
+  "Username": "Username",
+  "Insert your username": "Insert your username.",
+  "Password": "Password",
+  "Insert your password": "Insert your password.",
+  "Click to log in": "Click to log in.",
+  "Show login form": "Show login form.",
+  "Please log in!": "Please log in!",
+  "Open user menu": "Open user menu for {{session_info.username}}",
+  "Logout": "Logout",
+  "Click to log out": "Click to log out.",
+  "You have been logged out": "You have been logged out.",
+  "Logout failed": "Logout failed"
+}