Pango is at the top of the open source text/font stack. It's becoming the defacto on Linux/X11 and gaining traction elsewhere. It uses native engines (CoreFont on OSX and Uniscribe on Windows) where applicable. It has the ability to do multi-lingual matching and rendering, complex character shaping, and BIDI, amongst other things.
Benefits to the Student
Learn (at a high level at least), the ins and outs of modern font/text composition (one of the most taken-for-granted "arts" to computer programming currently). Gain experience in bridging between Smalltalk reifications of external libraries.
Benefits to the Community
If done right, since it does all of the rendering, a text editing ability that is beyond what any of the Smalltalks have, keeps them competitive with other offerings, and should be relatively applicable between different Smalltalk flavors.