This statement would likely be true in terms of economics, but political benefits, if any, would only be seen in the very long term.
In the short term, speaking a single language would be beneficial as soon as everyone was able to speak that language. There would no longer be time and resources lost on people trying to learn foreign languages. All people would be able to communicate with all other people, reducing barriers to trade between countries. These factors would mean that more resources would be available and trade would be easier. This would be economically beneficial.
Politically, however, there would likely be great animosity stirred up by this change at least for a while. People would be very angry at being forced to give up their native language. There would be problems because people would feel that their cultural distinctiveness was being taken from them. In the long term, common languages might lead to more understanding between various peoples, but that might not even happen. The political benefits, then, are less obvious than the economic benefits and are only likely to appear after a long time when generations have passed so people could get over feelings of nationalism.