The word "free" is often considered to be unclear, and ambiguous. As such, the word is often used in conjunction with the word "libre", as seen in this answer.
In the spirit of clarity, the word "libre" is often used to clear the alternate meaning of the word "free," so that the implication will be that of free as in speech, not free as in food. Free Software is often referred to as Free/Libre software, and the common acronym FLOSS, stands for Free/Libre and Open Sorce Software.
Therefore, if the word free is consistently added as a pair to the word "free", why doesn't the Free Software Foundation instead simply use the word libre? I can understand if there are considerable obstacles to make a complete, efficient transition to the clearer word libre, but I'm curious to see if the FSF has a stance on this.
Just to be clear, I am not asking why the FSF doesn't make the switch, but rather what their stance and efforts are, or have been.
Update: To counteract the fact that the FSF uses "free" because of it's implied meaning, The FSFLA (or Free Software Foundation Latin America) has named their linux kernel to be this: linux-libre.
More on the wikipedia article: Linux-libre