Message says: "Replace LANG part with your language code ..."
It seems, that there is no "LANG" text string anywhere but already replaced with the user language, see URL.
For testing change your user language.
If the replacement is automatically done the message should be rephrased I think.
Version: master
Severity: normal
URL: https://commons.wikimedia.org/w/index.php?title=TimedText:Neuroimmunological-Blood-Brain-Barrier-Opening-in-Experimental-Cerebral-Malaria-ppat.1002982.s024.ogv