Is Ajahn Thanissaro's translation incorrect speech? In my opinion it is a bad translation of musāvāda, which means telling lies, not merely saying something that is incorrect. Speaking falsehood, believe it to be true, but not intending to deceive is not telling lies. It may be incorrect and false, but its not musāvāda.
The five precepts are a pragmatic standard for lay people to follow. At the very least, they should abstain from telling deliberate lies, when asked about the truth of some matter. However, undertaking and observing the five precepts is just the basics, it is not yet enough to develop the Noble Eightfold Path in full.
From the description of Right Speech as a path factor, it is clear that gossip, back-biting, or slander, abusive speech, and idle chatter such as telling jokes and shaggy-dog stories are wrong speech. These three are also included in the ten kinds of immoral deeds (dasākuslakammapaṭhā), kammas leading to rebirths in the four lower realms. so a devout Buddhist should certainly abstain from these too. It is expressly proscribed when undertaking the
• • • • (Upasampadā: 24th June, 1979)