Sinn Fein MLA Conor Murphy has said an agreement on an Irish language act remains essential to any deal being done to restore the power-sharing Executive.
It comes after an interview by DUP leader Arlene Foster in which she insisted her party would not sign off on a stand-alone Irish Language Act.
Mrs Foster said speculation about what legislation might look like was "not grounded in any sort of reality".
She ruled out any law which would include bilingual road signs, compulsory teaching of Irish in schools, or quotas of Irish language speakers in the civil service.
“The talks are at a critical stage and Sinn Fein’s focus remains on achieving a deal to restore the political institutions," said Mr Murphy, who has been a main negotiator for Sinn Fein throughout the talks process.
"However they want to describe it, the DUP know that agreement requires an Acht Gaeilge.
“The DUP need to make up their mind up about whether they up for a deal or not.
“This is a time for leadership and calm heads and there is a responsibility on all involved not to react to some of the noise from people who simply don’t want an agreement."
Taoiseach Leo Varadkar and Prime Minister Theresa May were in Belfast on Monday in the hope a deal could be done.
Speaking inside Stormont House, Mrs May said: "It should be possible to have an Executive up and running in Northern Ireland very soon."