How likely is it that, on the court records, that says I cannot read or write, that the English merely assumed I couldn't read or write in English, but could I be literate in my own tongue?
I ask because my ancestry has a mention of my Irish ancestors being brought before a magistrate in County Cork on the charge of assaulting a dwelling, and a member of an Irish rebel group called the Whiteboys. How likely is it that my ancestors actually knew how to read and write in Irish, but not in English?
It is not impossible but it is fairly unlikely. According to Niall Ó Ciosáin, literacy in Irish tended to accompany that in English. People learned to read in English first and applied that knowledge to Irish texts. For that reason popular printed works were produced mostly in Roman rather than Irish characters.
Literacy is a slippery concept as it covers anything from basic ability to read a few phrases and sign ones name right up to being able to read and write complex texts. The statistics create a false binary whereas in reality people would have a wide variety of literacy levels depending on their education and how often they ever needed to read. For court purposes I expect it meant that your ancestor needed written court material read to him. In the 1841 census 53% of those over 15 years old claimed some literacy. This would have been significantly lower among poorer peasants for whom schooling was a double cost in payment to a teacher and hours of work lost. Irish literacy levels were lower than other parts of the UK but relatively high compared to similarly under developed parts of France or Italy.
Sources:
Niall Ó Ciosáin, VARIETIES OF LITERACY IN NINETEENTH-CENTURY IRELAND: GENDER, RELIGION AND LANGUAGE (https://www.academia.edu/41182545/Varieties_of_Literacy_in_19thc_Ireland) 2019
Cormac Ó Gráda, School attendance and literacy before the famine : a simple baronial analysis (2010) https://researchrepository.ucd.ie/handle/10197/2647