title: Drawing in NLTK with tkinter-canvas and exporting to postscript, some fonts are not shown
body: <p>This is related to the issue <a href="https://github.com/nltk/nltk/issues/2429" rel="nofollow noreferrer">https://github.com/nltk/nltk/issues/2429</a> .</p>
  <p>I will repeat the details of the issue here to get quicker replies from the community.</p>
  <p>I looked at the code of a drawing demo:</p>
  <p>nltk/nltk/draw/util.py</p>
  <p>Lines 2534 to 2538 in 33ac28c</p>
  <pre><code> cf = CanvasFrame(closeenough=10, width=300, height=300) 
   c = cf.canvas() 
   ct3 = TextWidget(c, &quot;hiya there&quot;, draggable=1) 
   ct2 = TextWidget(c, &quot;o  o\n||\n___\n  U&quot;, draggable=1, justify=&quot;center&quot;) 
   co = OvalWidget(c, ct2, outline=&quot;red&quot;) 
  </code></pre>
  <p>And trying to insert some Chinese characters in line 2537, I get the following picture:</p>
  <p><a href="https://i.stack.imgur.com/2unxm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2unxm.png" alt="enter image description here" /></a></p>
  <p>On the left hand side is rendered by the demo, the right hand side is using the button Print to Postscript.</p>
  <p>We can see that actually the rendering is successful as the bold song ti text 可以的 is shown.
  However, the exporting to ps failed. Not only the Characters but also some math symbols are not exported.</p>
  <p>But I am not good at tkinter, so my trial to fix this failed.</p>
  <p>I hope someone else can help to fix this.</p>