The new hub, Grand Central Station, is expected to cost about £340m.
There is still no date for the start of rail services but Translink insists it will be soon.
An Dream Dearg claimed the lack of Irish signage was against the wishes of the infrastructure minister, external, John O’Dowd of Sinn Féin, and Belfast City Council.
Speaking to News NI, Ciaran Mac Giolla Bhein from An Dream Dearg said the group is “incredibly disappointed”.
When asked if the group will be taking legal action, Mr Mac Giolla Bhein said: “We may well find ourselves going down a legal route, but hopefully it can be resolved before that.”
“This is not just a transport hub for Belfast, it is a transport hub for people from right across the island of Ireland and it’s important that it’s reflective of where we are as a city,” he added.
Translink has defended its handling of the issue and said that Irish will be among the languages used on “multi-lingual welcome signage”.
There has been no comment yet from the minister who oversees public transport, Sinn Féin’s John O’Dowd.
On Wednesday, News NI asked the Department for Infrastructure about the minister’s view on Translink’s decision, and whether or not he had the power to demand the use of dual-language signage.
In April, Belfast City Council approved a motion supporting “the installation of bilingual internal and external signage at Cros na bhFíodóirí – Weavers Cross – Belfast’s new Grand Central Station”.
In July, Translink’s chief executive Chris Conway wrote to the council saying that discussions were ongoing about signage with interest groups and political parties.
These included Conradh na Gaeilge and the Ulster Scots Agency, as well as the DUP and Sinn Féin.
Mr Conway indicated there was no consensus on the signage issue.
