use randomDistribution.frink

// Approximate letter frequency in English
dist = new randomDistribution
dist.add["a", 8.04]
dist.add["b", 1.54]
dist.add["c", 3.06]
dist.add["d", 3.99]
dist.add["e", 12.51]
dist.add["f", 2.30]
dist.add["g", 1.96]
dist.add["h", 5.49]
dist.add["i", 7.26]
dist.add["j", 0.16]
dist.add["k", 0.67]
dist.add["l", 4.14]
dist.add["m", 2.53]
dist.add["n", 7.09]
dist.add["o", 7.60]
dist.add["p", 2.00]
dist.add["q", 0.11]
dist.add["r", 6.12]
dist.add["s", 6.54]
dist.add["t", 9.25]
dist.add["u", 2.71]
dist.add["v", 0.99]
dist.add["w", 1.92]
dist.add["x", 0.19]
dist.add["y", 1.73]
dist.add["z", 0.09]

g = new graphics

g.font["SansSerif", "bold", .8 in]

for x=1 to 6
   for y=1 to 6
   {
      g.color[.8,.9,.9]
      g.fillRectCenter[x*1 in, y*1 in, .9 in, .9 in]
      g.color[0,0,0]
      g.text[uc[dist.random[]], x*1 in, y*1 in]
   }

g.show[]