Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
and make sure the TTF format has a mode of r-- and a modern version of the Freetype library. You also need a font that supports a Unicode encoding. The Helvetica font under Linux comes from the Ghostscript font collection. It may not support Unicode.