A ticket inspector’s bilingual greeting to a Flemish train passenger has created a political war of words – and an official complaint – in language-divided Belgium.

The country’s language watchdog is investigating after a Dutch-speaking commuter protested a conductor’s use of “bonjour” – French for “good morning” – to welcome him onboard during a rush-hour train from Mechelen, in Flanders, to the capital, Brussels, in October.

Writing on Facebook, Ilyass Alba, the French-speaking conductor, said that on the day in question he greeted passengers entering his carriage with a resounding “goeiemorgen, bonjour”.

The use of both the Dutch and French greetings was not good enough for one Dutch-speaking passenger, who told him off, saying: “We’re not in Brussels yet, you have to use Dutch only!”

The passenger was technically right, as under Belgium’s complex language rules conductors should in theory use both languages only in Brussels and a few other bilingual regions.

“The file is under review,” the Permanent Commission for Linguistic Control said, adding it would ask the national railway operator, SNCB, for more information on its enforcement of language policies.

The affair has caused a stir in Belgium, where politics largely follow a linguistic divide pitting northern Dutch-speakers against French-speaking southerners.

Georges Gilkinet, the transport minister and a French-speaking environmentalist, came to Alba’s defence, saying that in a small country such as Belgium, regional borders are crossed all the time.

SNCB conductors should prioritise giving “a quality welcome” and ensuring all passengers are “properly and fully informed”, Gilkinet said after being quizzed in parliament over the issue. “Using several languages to say hello does not shock me,” he added.

Some Dutch-speaking politicians disagreed.

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“We can’t just throw our language legislation overboard like that,” said Sammy Mahdi, head of the CD&V, a party of Flemish Christian democrats.

SNCB, for its part, called for “more flexibility” in applying language rules. “Saying hello in several languages is just nice, we can only thank our conductors for that,” a spokesperson told AFP.