I wanna have the James Joyce quote "Mistakes are the portals of discovery" in black gaelic. Thank you ^.^

Not sure what you mean by "black" Gaelic, but here is an attempt in Irish Gaelic:

Bíonn na meancóga mar dhoirse ar an bhfionnachtan.

Await confirmation or correction ...

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

or possibly -

Tá dearmadaí mar dhoirse eolais.

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It is recommended that you always wait for three to agree on a translation.
I speak Connemara Irish, and my input will often reflect that.
I will do an mp3 file on request for short translations.
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I'd say ...mar dhoirse...