German overtakes French as EU's second most popular language

2 or 2.5 million is still arbitrary.

It's always better that 30.000

that = than

I'm sorry, but you don't seem to have much of a clue about statistics. Even a sample size of 30000 is HUGE; the probability of the deviation from the an actual percentage of 25% being more than 0.5 percent points is less than 5%. Of course, the smaller percentages are less accurate and that's probably the reason why they chose such a big sample.

The only problem is that people might not be telling the truth claiming that they have learned a language they actually haven't; but I'm sure they know how to compensate for such effects considering that they have the resources to call 30000 people.