added missing language key

public/language/en-GB/error.json

@@ -21,6 +21,7 @@
 	"invalid-username-or-password": "Please specify both a username and password",
 	"invalid-search-term": "Invalid search term",
 	"invalid-url": "Invalid URL",
+	"local-login-disabled": "Local login system has been disabled for non-privileged accounts.",
 	"csrf-invalid": "We were unable to log you in, likely due to an expired session. Please try again",
 
 	"invalid-pagination-value": "Invalid pagination value, must be at least %1 and at most %2",