[R] How could plot a chart with some Chinese's words text?

[Ken Lee]

Dear all,
      I want to plot a chart title with some Chinese words at unix system, but I do not how to do.
first, it is no problem when  I use write.table like:
 
a<-"中文"
write.table(a,file="z.txt",sep="\t") 

second, I try 

bitmap(file="z.png")
plot(1:10,main=a)
dev.off()

I can't get a chart with the right title ="中文" 

Why have this difference?

Thanks a lot

ken