[igraph] Problem with displaying vertex's label text in Chinese characters

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Dear,

        I use python-igraph-0.7 on Ubuntu to draw graph.  To display the vertex's text, I add its label attribute . As the text are Chinese characters of 'unicode' type (not 'str' type),  I encode them by "UTF-8". But when the graph is shown, the Chinese characters are show as the small squares, unreadable codes. What's wrong with this?thanks very much. 

      Best Wishes!