This article in the NY Times about a study published in Nature discusses the FXP2 gene. People with mutated FXP2s "have severe problems in articulating and understanding speech." If you put the human version of FXP2 into a mouse, it squeaks differently and has changes in brain structure. What this study did was put the chimp version into human neurons (not while they were in a human). They found that FOXP2 "controls the activity of at least 116 other genes," turning them on or off. Busy little chunk of code.
It is not the only gene (or set of genes, if you count the 116 it controls) involved in language, but it's a step in understanding the genetics of speech and language.