Ooh... Hadn't considered that. I thought it was a cultural thing, but I like the idea of it being a consequence of having the herb applied to him.
I think it still could be a tribal thing with the EW picture of Killmonger with a signet ring similar to T'Chaka's in CW.
They've been quite secretive about Killmonger's backstory (per usual, it is Marvel Studios), Nate Moore's comments about the plot dealing a lot with family ties, The voiceover of T'Chaka talking about the hardship of a 'good man' being king...
Wild speculations on my part, but bear with me.
What if Killmonger's origin has been conflated with 616 Hunter or Ult. M'Baku Udaku? He is a son, adopted or blood, of T'Chaka's. The tribal scars/ring being marks of belonging to the royal line. So when he presents himself, he's not a mere political dissenter. He has a legitimate claim to the throne, which leads to the gauntlet being thrown down of tribal combat to decide the fate of the kingdom.
And/or MCU Killmonger was working in a White Wolf-type capacity for T'Chaka unbeknownst to anyone (This would really harken back to the 'good man' part, if T'Chaka had him doing his wetwork in the shadows.) Look at how few areas we've seen Klaue. The attack at the casino, the interrogation by Ross and I think that's it so far.
What if Killmonger isn't breaking Klaue out, but kills him (He's a known threat to Wakanda so he has to be handled; It's what a self-proclaimed 'patriot' like WW would do) and ultimately gets arrested/surrenders? Then T'Challa goes 'This man will face justice in my country' and Ross, being more suspicious following CW, wants to see what Wakandan justice means exactly, and using the Sokovia Accords as leverage, gets to go along for the ride now. Meanwhile, being extradited into Wakanda is exactly what Killmonger wanted all along so that he could make the reveal of his claim to the throne?