Yeah, that looks like Google Translate all right. You won't be surprised to discover that neither of these phrases is remotely grammatical.
The issue is that Irish altogether lacks a pluperfect. Even speakers of Irish English avoid it. There are a couple of constructions in Irish called the "perfect", but their use is limited to events completed in the present. So you can say "Táim t'réis déanamh dearmaid ar a ainm" to mean "I've just forgotten his name" but it doesn't make much sense to put this into the past tense without the right narrative context.
So you would simply say "I forgot" (rinne mé dearmad--or, the way I speak Irish, do dheinis dearúd) and rely on context to disambiguate whether you've since remembered again or not. Another possibility is to use the imperfect, i.e. déanainn dearmad. This makes it clear that your days of forgetting are over, but it implies that forgetting was something habitual, i.e. you would forget it, remember, and then forget again.
Here's the full answer I got on the other board. My own answer had been lacking necessary detail.
And another paragraph, added later.
SonicRed might also find it useful to know that rinne mé dearmad is Standard Irish whereas do dheinis dearúd is Munster dialect (specifically West Muskerry).