Fianna Fáil Senator Brian Ó Domhnaill has brought a High Court challenge to an investigation by the Standards in Public Office Commission into alleged duplication of expenses claims.

The action relates to an investigation concerning travel and subsistence claims made by Mr Ó Domhnaill between 2006 and 2007, when he was a member of Donegal County Council.

The commission was due to begin a public session concerning the expenses matter last June, but that did not proceed after Mr Ó Domhnaill secured leave from the High Court days earlier to bring his challenge.

In his judicial review proceedings, Mr Ó Domhnaill claims the commission is not entitled to deal with the matters on grounds, he claims, they arose from an anonymous complaint by a member of the public.

Alternatively, he wants orders requiring the case to be heard by a commission comprising members who are bilingual and able to conduct and understand the proceedings without the assistance of an interpreter.

Unless the tribunal is bilingual, his rights as an Irish speaker will be infringed, it is claimed.

He alleges he will be disadvantaged if an interpreter is necessary to translate the evidence and submissions given on his behalf in Irish.

Translated evidence is not similar to direct evidence and he would be marginalised, he claims.

The refusal to provide a bilingual tribunal amounts to treating him as a foreigner in his own country instead of a person who speaks the first official language of Ireland, he argues.

The proceedings, brought against the commission, the Minister for the Environment and the State, were conducted in Irish before Mr Justice Gerard Hogan over two days.

After hearing final submissions from the sides, he reserved judgment.

In opposing the case, the commission and State contend the complaint being investigated by it relates to alleged duplication of expenses claims and the investigation is in the public interest.

The commission said the complaint before it was made in a letter dated 28 May 2012 sent to it by the Mayor and County Manager of Donegal County Council following an investigation by the two men of a referral made to them by the Ethics Registrar of the Council.

While acknowledging that information in an anonymous letter had prompted the Ethics Registrar to examine matters, the commission contends the complaint being investigated by it is not a referral of that anonymous letter by the Mayor and County Manager, but rather a complaint by those men arising from their view certain specified acts set out in their report may have been done by Mr Ó Domhnaill.

The commission also denies the senator is entitled to orders requiring members of the commission hearing the matter should be bilingual.

It insists it has made every effort to facilitate his wish to conduct his side of the hearing in Irish, but there is constitutional right for citizens to a bilingual court or tribunal who choose to conduct their business in Irish.

As there is no requirement in the Constitution for judges or members of the Oireachtas to be bilingual, that requirement should not be imposed on commission members, the defendants insist.

Mr Ó Domhnaill had from August 2011 until last March, when he changed solicitors, engaged with and addressed matters related to the expenses issue in English, it is claimed.