A Brit (or Briton)
A Japanese person/man/woman etc
A Chinese person/man/woman etc
A Spaniard (whereas Spanish is the adjective)
A Swiss person/man/woman
And there are a few that I don't even know if there is an adjective:
Greenland (a Greenlander)
Iceland (an Icelander)
New Zealand (a New Zealander)
The only connection in the first list is that they all end in "n", whereas French, Dutch, Swiss etc don't.
I don't think I would say "I met a Chinese last night". I would say "I met a Chinese person/man/woman etc last night". But I would have no problem with "I met an Italian last night".
Student or Learner