This is most likely a font problem. The default font igraph is using to draw the text labels does not have the characters present. I'm not sure how to switch the font for raster images (png, etc.), but it is easy to work around for SVG.
For example,
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import igraph
g = igraph.Graph()
g.add_vertices(3)
g.vs[0]["label"]="母"
g.vs[1]["label"]="私"
g.vs[2]["label"]="ABC"
g.add_edge(0,1)
g.add_edge(1,2)
g.add_edge(2,1)
layout = g.layout("circle")
g.write_svg("tmp.svg", layout = layout)
generates a file called tmp.svg. Opening this in any standard text editor (e.g. gedit) it is simple to find and replace all instances of the default font for another font that supports Chinese characters. In my installation I had to search for "font-family:Sans" and replace "Sans" with another font.
Cheers,
Scott