There can't be a "definitive" translation, because the pseudo-Latin precedes the popularity of the English. That second link you offer is actually good. Harry Beard offers Noli nothi permittere te terere.

Personally, I could see a few tweaks. Instead of nothi, I'd subsitute it with spurii. Also, te terere sounds clumsy; I'd be tempted to use attere instead.

Alternatively, to be less literal, I'd opt for: Ne terant te spurii. Typically for "let not" Latin employs ne + the subjunctive. Compare that with e.g. Cicero's De Legibus 2.16.41, donis impii ne placare audeant deos ("let not the wicked dare [to try] to appease the gods with gifts").

There can't be a "definitive" translation, because the pseudo-Latin precedes the popularity of the English. That second link you offer is actually good. Henry Beard offers Noli nothi permittere te terere.

Personally, I could see a few tweaks. Instead of nothi, I'd subsitute it with spurios (needs the accusative). Also, te terere sounds clumsy; I'd be tempted to use attere instead.

Alternatively, to be less literal, I'd opt for: Ne terant te spurii. Typically for "let not" Latin employs ne + the subjunctive. Compare that with e.g. Cicero's De Legibus 2.16.41, donis impii ne placare audeant deos ("let not the wicked dare [to try] to appease the gods with gifts").