Crypto-nationalists in the DUP such as Nelson McCausland who emphasise Ulster-Scots do so based on the fallacy that if a people have a distinctive culture and language, they form a nation.
In DUP logic, since the Protestant majority of Northern Ireland claim to have a so-called language in Ulster-Scots, they form the Northern Irish nation. Where does that leave the Irish Catholic people? The truth of the matter is that the people of Northern Ireland speak a regional version of the English language with an Ulster accent so they have a regional identity, not a national one. The same could be said of the people of Connaught, Leinster and Munster.
To belong to a nation, the people must have an agreed national constitution. This can be illustrated in the constitutional histories of Australia and Canada. Prior to the 1980s, both Australia and Canada had cultural and language identities but they were dominions not nations.
In the 1980s they were granted their own constitutions under the control of the people in the Australia Act 1986 and in the Canada Act (Patriation) 1982. They were then sovereign independent nations within the Commonwealth of Nations.
The same fallacy as the Ulster-Scots underlies the Irish language. Sinn Fein believes that in promoting the Irish language they are promoting Irish nationhood.
Both Ulster-Scots and the Irish language should be preserved but Irish nationhood will require its own written constitution for all Ireland defined in the National Government of Ireland Act to become an all Ireland agreed nation.