Hi! I happen to be doing a serious reading of the original Rheims translation of the New Testament, so I think this is a question that I have some confidence to answer.
- is discere a typo for dicere? or is “say” a typo for “learn”?
I agree with jeidsath, that the original Rheims translation, which is the base for the Challoner revision as provided here, in all the likelihood, has used a different Vulgate than that we have today.
“[N]o man could say the song” is in the original Rheims translation of the New Testament published in 1582, therefore not a typo, but reflects certain reading of Vulgate we do not have today (but banished in the footnote of some critical edition eg. Weber-Gryson). Keep in mind that the translators did not even have Sixtine or Clementine Vulgate, which published a few years later, and in their copy (or copies) of the Vulgate, Rev 14:3 probably reads “nemo poterat dicere canticum”.
It seems that even the Rheims translators themselves realized this reading was dubious (but chose to follow it anyway), since the Greek reading “learne μαθεῖν” was given in the marginal note:
https://archive.org/details/1582DouaiRheimsDouayRheimsFirstEdition3Of31582NewTestament/page/n700
Now,
i) the Challoner revision, notwithstanding its numerous changes to the original Rheims NT (some might even go so far as to say it is a totally different translation), for some reason, maintained this particular reading. And
ii) the publisher of the Latin-English bible today normally uses an updated version of the Vulgate for the latin text (most Vulgate text used today are the result of 19th and 20th century critical scholarship),
thus the discrepancy in the text.
- is “purchased’” a typo for “redeemed”? If not, what does “purchase” mean in this context?
Here again I agree with jeidsath and have not much to contribute.
I am still learning Greek and in no place to judge, but I think the Latin is a pretty accurate translation of the Greek original (reads ἠγορασμένοι, the perfect passive participle for ἀγοράζω, which means “I buy”, so the Latin empti, perfect participle of emo, “I buy”. Word of the same root has been thus consistently translated, as in Rev 3:18, Rev 13:17 and other places). The problem arises in English rather than in Latin. However since redeem itself comes from re + emere, meaning “to buy something back”, it should not be so surprising to see the word “purchase” here.