The Eurobarometer 386 survey asked people about their language abilities and attitudes to language learning. One of the questions asked was as follows:
The interviewees had the option to choose up to two languages they considered useful, where none was also an option.
Quite unsurprisingly, English dominates the map, with Luxembourg being the only country where it is not the most popular foreign language (Luxembourgers prefer French due to their strong economic and cultural bonds with France and Belgium). French was also preferred in Ireland and the UK, which is logical, since English is mostly spoken as the first language there and thus could not show up in the statistics.
The map of the language voted second most useful (see below) turns out to be much more interesting. In Bulgaria, Greece, Italy, and Portugal, more people actually chose the option “none / no other language” than the language shown in the map. Note that the caption “French” for Belgium is to be understood as the foreign language of choice of the Dutch-speaking part of Belgium.
As you can see, trends in usefulness of languages are mostly set by geographical proximity—inhabitants of countries sharing a border with France prefer French, countries sharing a border with Germany and Austria prefer German, and countries Sharing a border with Russia prefer Russian.