Sinn Féin has branded as "insulting" a claim by DUP leader Arlene Foster that the republican party is using the Irish language to "humiliate" unionists.
Senior party figure John O'Dowd criticised Mrs Foster's remarks and said she was living in a "fools' paradise" if she thought powersharing could be restored at Stormont without progress on the language question.
The DUP's refusal to sign off on a Sinn Féin demand for a free-standing piece of legislation that would enshrine statutory protections for Irish speakers is the key roadblock preventing the re-establishment of a coalition executive.
Talks to restore powersharing, which collapsed at the start of the year, remain stalled with little sign of progress on the horizon.
Northern Ireland Secretary James Brokenshire has warned the north is on a "glide path" to a form of direct rule from Westminster if the impasse is not resolved within weeks.
While the DUP is prepared to countenance legislative protections for Irish as part of a wider piece of legislation that also incorporates the Ulster Scots culture, the party is set against a free-standing Irish language act.
Mrs Foster repeated that stance in a radio interview on Sunday.
She told BBC Radio Ulster: "Sinn Féin has decided to ring-fence a free-standing Irish language act in a way that frankly makes it impossible for those who want to move forward but see this is just being used as a way to humiliate unionists and those of us who believe in a British way of life."
Two weeks ago, Mrs Foster said the Irish language itself threatened no-one and called for an immediate restoration of powersharing and a parallel negotiation process to deal with the language issue and a series of other disputes between the two main parties.
Mr O'Dowd said her remarks on Sunday showed that forming an executive before the issue was dealt with would have been "folly".
"The parallel negotiations would have went nowhere and there was no intentions of resolving the outstanding issues, including an Irish language act," he said.
"If the DUP want back into the executive and they are serious about reforming an executive then they have to understand the only basis on which that executive will be formed will be on the basis of equality, rights and respect and entitlement for all, including the Irish language speaking community."
He added: "Quite frankly Arlene's Foster's comment about Sinn Fein's motivation behind the Irish language act are quite simply insulting.
"They quite clearly haven't been listening to what Sinn Féin have been saying to them, about the motivations behind an Irish language act the reasons for an Irish language act - the need to build a society based on the rights and entitlements of all citizens."
Formal roundtable talks involving the five main Stormont parties and the UK and Irish governments have still not resumed after they were parked for the summer.
Sinn Féin and the DUP are instead engaged in a series of private meetings - discussions that are due to continue this week.
