But the measure was fiercely opposed by the right, with lawmakers from far-right Vox walking out as members of Sánchez’s Socialist party addressed the assembly in Galician.

They also returned the earpieces that would allow them to hear a simultaneous translation.

“We don’t want to be complicit of the breakdown of our co-existence,” the head of Vox’s parliamentary group, Maria Jose Millan, told reporters.

Vox rejects Spain’s current system of devolved regional powers and has proposed a national referendum to ban separatist parties.

The main opposition conservative Popular Party (PP) meanwhile demanded that the use of minority languages in the assembly only be allowed once the rules on their use are formally approved on Thursday.

Catalan, Basque and Galician, which are spoken in various regions, are all classed as co-official languages in Spain, where the official language is castellano, or Castilian Spanish.

Alongside Spanish, these languages are taught in schools and used in the respective regional administrations and parliaments in Catalonia in the northeast, the Basque Country in the north and Galicia in the northwest.

Being permitted to use these languages in debates in the Spanish parliament has long been a demand of nationalist parties in these regions.

“This is a historic day… Finally the rights of Catalan speakers are being respected,” Miriam Nogueras, a Catalan lawmaker from Carles Puigdemont’s hardline JxCat party, said outside parliament.

READ MORE: Why Spain has allowed regional languages to be spoken in Congress

JxCat unexpectedly emerged as kingmaker following Spain’s inconclusive July 23rd election.

It has since laid out a string of demands in return for its support to ensure Sánchez, currently in an interim role, can stay on as prime minister.

Allowing the use of such languages in the assembly was one of JxCat’s demands in exchange for its support to ensure the election of Francina Armengol as parliamentary speaker, the candidate from Sánchez’s Socialist Party.

Puigdemont headed Catalonia’s regional government during the botched 2017 independence bid that sparked Spain’s biggest political crisis in decades.

He fled Spain shortly after to avoid prosecution and has since lived in self-imposed exile in Belgium.

Spain’s EU language debate

JxCat also demanded Madrid ensure that Catalan, Basque and Galician were recognised as official languages of the European Union, a question which was being debated by the bloc’s top diplomats earlier on Tuesday.

The EU currently has 24 official languages, although there are around 60 minority and regional languages in the bloc.

The inclusion of any additional official languages must be agreed unanimously by all 27 member states.

But the proposal drew objections, with the EU debate postponed as ministers from the bloc sought more time to mull over the issues.

READ MORE: EU States reluctant to add Catalan as official language

Spain’s general election resulted in a hung parliament.

The right-wing Popular Party won most votes and its leader, Alberto Núñez Feijóo, has been tasked with forming a government, despite lacking a working majority within the 350-seat assembly.

Should he lose the parliamentary vote to become prime minister on September 27th, the task of forming a government will pass to Sánchez.

Sánchez will then have two months to piece together a governing majority – which will only be possible with support from JxCat’s seven lawmakers.

If he also fails, Spain will have to call new elections, probably in January.