Was Irenaeus' Work Against the Heresies Originally Written in Latin, Greek or Aramaic?

I have always wondered what language the Refutation and Overthrow of Knowledge Falsely So Called was originally written in. Irenaeus confesses at the beginning of the collection which is worth taking a second look at:

Thou wilt not expect from me, who am resident among the Keltae, and am accustomed for the most part to use a barbarous dialect, any display of rhetoric, which I have never learned, or any excellence of composition, which I have never practised, or any beauty and persuasiveness of style, to which I make no pretensions [i.intro.3]

The passage is commonly read as referring to Irenaeus' alleged status as bishop of Lyons, southern France here being referenced as 'the land of the Celts.'

But if the passage was originally written in Greek the original term would have been Keltoi which means 'stranger people' or barbarians. Whenever Greeks encountered foreign people they would call them Keltoi or Galatai which is were undoubtedly the group that was addressed by the Apostle in his Epistle to the Galatians.

Was Galatian a technical term for Christian? It seems to be. In the often ignored Acts of Archelaus, the bishop of Harran cites the Epistle to the Galatians against Mani and then proceeds to use the term 'Galatian' as technical term meaning 'Christian':

And when the Galatians are minded to turn away from the Gospel, he says to them: I marvel that you are so soon removed from Him that called you unto another gospel ... None of your party O Manes, will you make a Galatian; neither will you in this fashion divert us from the faith of Christ. [Acts of Archelaus 35,36]

Bauer points to strong evidence which suggests that the Catholic tradition was identified as 'Palutians' in the Osroene. My guess is that the term goes back to the Aramaic ger but this is all mere guesswork.