It was the graphics card driver fault. I noticed the rendering was pretty slow. The tested the driver with glxgears, I had very low FPS (around 50). So I removed the radeon and drm drivers and switched to AMD fglrx driver. Now I have around 4000 FPS, the labels are there, and 0ad simply blows my mind!
Hello, I built 0ad revision r09530-alpha from sources on debian weezy on amd64 architecture. I can see no labels on fields and buttons. Regards, Carlo.