Does anyone remember River of Adventure? Now that one really was incredibly racist (and gender-rigid). Smelly black child is given a much needed bath and follows the Fab Four around like an adoring pet dog. Indian boy-prince has long hair and gets ENDLESS negativity about it from other characters and the author. Etc. etc. The usual tropes.
That was the one I knew least because for some reason I never owned a copy and our local library didn't have it -- but I read it with my son recently, and was gobsmacked. Less for the depiction of the (Syrian?) child, which was pretty much par for the course for EB, but for the extent to which Tala, the local boatman, who is with the children for most of the adventure, is infantilised because he's a 'native', and it's seen as entirely natural for English children to effortlessly dominate an adult man with local knowledge. (Mind you, you could say the same thing for the depiction of David the shepherd in The Mountain of Adventure...)
(Was the prince not Gussy in The Circus of Adventure? Who, because he is a foreigner, is a crybaby and asks for 'pig meat and cream'? and is forced, to everyone's amusement, to dress up as a girl in a dress and hair-ribbons when the children hide out in a Tauri-Hessian circus? Because clearly this is entirely different to Dick or Julian having to compromise their dignity and disguise themselves in hair ribbons and a dress, or Fatty cleverly disguising himself?)
Actually, EB seemed to have a real thing about boy foreigners not being as 'manly' as their British equivalents. Prince Paul and Gussy are both presented as childish and rather drippish, compared to Jack/Mike/Other Jack/Philip. Or they're Faithful Native types like Mafumu in The Secret Mountain.
Tammylan is described as having long hair and beard and wearing 'queer clothes', but in the illustration to the edition on Faded Page, he has a short back and sides and is wearing a pinstriped suit and a fedora. 