The Sinn Féin leader says a draft deal "did not involve at any stage making Irish compulsory"
Sinn Féin says it is up to the DUP to explain why talks over restoring a power-sharing executive collapsed.
The party says there was a draft agreement with the unionists, which included an Irish Language Act.
Yesterday, the DUP said that was the stumbling block which led to talks ending, with Arlene Foster suggesting "there is no current prospect of these discussions leading to an Executive being formed".
Sinn Féin leader Mary Lou McDonald, however, says a deal was ready to go and accused the DUP of collapsing the talks process.
Deputy McDonald said: "It is up to Arlene Foster to explain this given that the DUP and Sinn Féin leaderships had achieved an accommodation across the issues involved.
"In fact we had a draft agreement by the end of last week. At that time we advised the DUP leadership that the deal should be closed before those opposed to it could unpick what we had achieved."
She explained that copies of the draft agreement text would be sent to both the British and Irish governments, and other political parties in the North and Republic would be briefed on its content.
However, the new party leader said the document would not be publicly published in order to give future talks "the best chance to succeed".
On the subject of the Irish language, Deputy McDonald said: "[The deal] did not involve at any stage making Irish compulsory or applying quotas to public services. This was not a consideration."
Meanwhile, the DUP's deputy leader Nigel Dodds claimed the Sinn Féin 'propaganda machine is in full flow'.
He said in a statement: "Arlene Foster was right to call time on the talks. We want devolved government but not at any price.
"Sinn Féin collapsed the institutions thirteen months ago and arrived with a shopping list of demands before restoring the Executive. They wanted a one-sided deal which could not have commanded the support of unionists. That’s not acceptable."
Northern Ireland has been without a power-sharing government since the collapse of the Stormont Executive in January 2017, amid a scandal over a botched renewable heat scheme.