The 20-year-old livewire is showing golden scoring touch as the Socceroos build towards the World Cup in the US, Mexico and Canada, which kicks off in June.
Charlton took the lead through Matty Godden, who made an instant impact after being substituted on just after the hour mark at Vicarage Rd on Monday (Tuesday AEST).
But Watford were more than good value for their leveller, with Irankuda converting in emphatic fashion.
The Australian's goal follows hot on the heels of his double for the Socceroos in the recent friendly against World Cup debutant Curacao in Melbourne.
Charlton were indebted to goalkeeper Will Mannion for holding on for a draw. Mannion made a string of saves for the southeast Londoners, who extended their unbeaten away run to six matches.
Godden struck with his first touch after being subbed on before a Harry Clarke long throw in the 62nd minute. Kayne Ramsay flicked the ball on and the frontman produced a perfectly executed right-footed strike past Egil Selvik.
Irankunda, who also hit the crossbar with a swerving strike in the second period, levelled after 74 minutes, racing on to a deft through-ball from Louza to rifle emphatically into the bottom left corner of the net.
The Australian celebrated in familiar fashion with an acrobatic backflip, much to the delight of the home fans.
Mannion continued to be kept busy and only a plunging save to his right kept out another attempt from Irankunda.
After the match, Watford coach Ed Still heaped praise on the young Socceroo.
"Nestory is a fantastic talent,'' Still said.
"What I keep saying to him is that we don't want to just see that in glimpses or moments. What separates special players from good players is they are not just doing it in glimpses. But that reflects a little bit on the consistency of the team's performances.
"He has created four or five good chances and he has converted one. What he also does is create space for others."
- with AAP
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