MathTexEngine only knows Computer Modern, which doesn’t have the characters you want. Using Label or Annotate you can build the title from pieces, and you can specify the font you need for each piece. It’s awkward because you have to fiddle with the spacing, but here is one way:
f = Figure();
lines(f[1,1], 1:2π/1000:2π, sin.(1:2π/1000:2π))
Label(f[0,1], "中文"; padding=(1.0, 1.0, 1.0, 200.0), tellheight=false, tellwidth=false)
Label(f[0,1], L"$\sin$"; padding=(55.0, 1.0, 1.0, 200.0), tellheight=false, tellwidth=false)
f
This gets you:
(I should note that I’ve just started to dip my toe into Makie, so there are probably much better ways to do this.)