Demand has risen steadily over the past 10 years, with close to 5,000 pupils now registered for French classes at the 'Alliance Française' in Brussels, up from less than 2,000 a decade ago, Lagnau told EurActiv.
This is despite the fact that usage of French has declined among EU staff, with most internal documents at the European Commission now drafted in English.
"It is undeniable that 'globish' has slowly imposed itself as the everyday language, to the detriment of French", says Lagnau, who leads the Brussels chapter of the 'Alliance Française', a public association promoting the French language and culture worldwide.
A return to "more balance" between languages now seems difficult to envisage, Lagnau admits with a sense of pragmatism.
With 27 member countries and 23 official languages in the European Union, French has largely lost its initial supremacy to the benefit of English, which has become the de facto working language in the EU institutions.
Dennis Abbott, spokesperson for EU Education Commissioner Androulla Vassiliou, in charge of multilingualism, confirms that "English is by far the most used language" in the EU executive.
The statistics speak for themselves. In 2011, English was the source language for 77.04% of all texts submitted to the European Commission's in-house translation services, up from 74.6% in 2009, Abbott said. By comparison, the position of French has continued to erode, representing only 7.13% of source texts, down from 8.32% in 2009. German, meanwhile, is confined to a marginal role, representing only 2.74% of source texts, despite being the single most spoken language in the EU, with almost a 100 million native speakers.
EU Court of Justice: A 'bastion' for French
These figures would make depressing reading to anyone promoting linguistic diversity. But Lagnau sees a silver lining too. The figures, he says, need to be nuanced as French remains the official language of the European Court of Justice and is widely used in some Commission departments such as the agriculture directorate.
To Lagnau, these are like "bastions" for French. And although the language of Molière is now rarely spoken in EU meetings, he says it has remained important in "corridor conversations" and in some expert groups headed by French officials where exchanges are made easier by a "linguistic connivance".
Moreover, ignoring French completely would be "a handicap" for officials looking to make a carrier in Brussels, especially in the European Commission where French is the second working language.
In fact, the erosion of French as a working language in the European institutions has even had a paradoxical effect, Lagnau points out. With fewer speakers around, demand for French classes has tended to increase in EU circles, he says.
From 1,826 pupils in 2001, the number of learners has risen to 4,797 in 2011, according to the latest statistics of the Alliance Française. Of those, 657 were diplomats and 17 are working at NATO's Brussels headquarters, Lagnau indicates. The rest are people associated with the diplomatic life in Brussels understood in the wider sense – spouses of expats or employees of international companies.
"Demand is growing," confirms Lagnau, citing as evidence "the number of hours sold, which is steadily increasing by almost 5% every year for over 10 years."
"We are therefore faced with an interesting paradox: while it is less used now in institutions, demand for French classes comes in high volume after all!"