ENV["GKS_ENCODING"]="utf-8"
using Plots
gr()
plot(1:5, 11:15, title = "τ is twice as good as π")
and these seem to work as well:
plot(1:5, 11:15, title = "τ is twice as good as π", fontfamily="Times")
plot(1:5, 11:15, title = "τ is twice as good as π", fontfamily="DejaVu Sans")
plot(1:5, 11:15, title = "τ is twice as good as π", fontfamily="New Century Schoolbook Roman")