Spain's demand for Catalan, Basque and Galician to become official EU languages faced opposition on Tuesday as the bloc's member states fear any such move will trigger a domino effect.
The headache for the EU began after Spanish Prime Minister Pedro Sanchez failed to score a victory in July elections and sought the support of Catalan separatists to stay in power.
Spain has taken advantage of its EU presidency to put the language issue on the agenda of a European ministers' meeting in Brussels on Tuesday, but Madrid's insistence is frustrating the bloc.
The European Union currently has 24 official languages, although there are around 60 minority and regional languages in the 27-nation bloc.
All legal EU documents -- treaties, laws and international agreements -- must be translated into the 24 languages and there must be translation available in them at leaders' summits and ministerial meetings.
Any additional language must be agreed unanimously by all 27 member states.
The Swedish government has said it is hesitant and has called for a study into the "consequences for efficiency of the union's work".
"There are many minority languages within the European Union that are not official languages," Swedish EU Affairs Minister Jessika Roswall told reporters on Tuesday.
EU ambassadors last week said the Spanish request raises "legal, administrative and budgetary questions" that must be carefully looked at before any decision.
What worries many in Brussels is that if they give ground to Spain, there could be similar demands from people who speak regional languages elsewhere in the EU.
Spain says it will cover the costs linked to translation, but without providing detailed figures.
"With regards to the Spanish proposal, we believe that it needs really very careful consideration," said Croatia's European Affairs Minister Andreja Metelko-Zgombic.
Catalan, Basque and Galician have official language status in Spain.
"We are not talking about minority languages," Spain's foreign minister Jose Manuel Albares said in Brussels.
"Catalan is spoken by more than 10 million people, which places it above many of the languages that are currently official and many of the languages of the representatives who will be around the table this morning with me."
According to the Spanish Statistical Office, 9.1 million people speak Catalan, while 2.6 million and 1.1 million speak Galician and Basque respectively.