Distance between vertex and label, size of label font and angle of label can be defined using keywords, but font of labels doesnt seem to be able to be defined. It seems that in igraph in R, fonts can be defined,but in Python the keyword seems useless.
The plotting backends in R and Python are completely different, so it is not guaranteed that the same keywords work for both backends.
For what it's worth, changing the font in Python is not supported because the underlying drawing backend (Cairo) has no standardized way of dealing with fonts on different platforms. You might be able to get around with a workaround posted in this answer on Stack Overflow (but this might or might not work on your platform, depending on what the Cairo implementation supports there):
All the best,
T.