Yes but Ndombele has already spent a couple of years playing in France - and I'd guess the % of non white populations of France and Britain are probably pretty similar, with London will have a higher % of non white population than the rest of UK.
So if Ndombele was happy enough in France with (lets say as an example) 1 in 8 people being BAME (and nothing to suggest he wasn't) then Britain wouldn't be such a change, other than of course language.
And Spurs as a club has had black players for years - Garth Crooks for example was a famous player for us in the early 80's and wasn't the first and one of our legendary captains in Ledley King more recently - so its not as if Ndombele is any way unusual in his ethnicity.
So whilst I'd give you the language barrier, as it must make talking to team mates a bit more difficult in the early days, its not as if he'd be the first Spurs player not fluent in English (and at least he has a few other French speakers in the team to help - Lloris, Sissoko, Aurier to name 3 and Jesus first team coach is fluent in French, not sure skin colour is more important than a 1001 differences any player wont find in changing country. Even down to needing to learn how to drive on a different side of the road or finding pubs in UK rather than bars and cafes in France...….you name it