Update lang-en.json and assets

gui/assets/lang/lang-en.json

@@ -1,4 +1,5 @@
 {
+   "A device with that ID is already added.": "A device with that ID is already added.",
    "A negative number of days doesn't make sense.": "A negative number of days doesn't make sense.",
    "A new major version may not be compatible with previous versions.": "A new major version may not be compatible with previous versions.",
    "API Key": "API Key",