Comment by adrian_b

I believe that the only useful form of the antique books, such as those originally written in Latin or Ancient Greek, is a bilingual edition, like those provided by the Loeb Library collection.

For Euclid's Elements, there is this excellent and free bilingual edition due to Richard Fitzpatrick:

https://farside.ph.utexas.edu/Books/Euclid/Euclid.html

The bilingual editions are useful even for people who do not know and do not intend to learn the original language, because they still allow them to discover which were the original meanings of many old words that are still in use today and to investigate the real meaning of certain paragraphs of interest, where an English translation may be unable to provide the correct meaning, without a very long commentary about the context. Moreover, in the case of books like those of Euclid, an non-specialist translator, i.e. a non-mathematician, will frequently make mistakes that can be discovered by a specialist, i.e. mathematician, who can compare the original and the translated text, even when the specialist has only little knowledge about the ancient language.

From Euclid's Elements, I consider that there are 2 sections that have retained most of their importance until today, and which are the most instructive: the 2 sections with definitions, the first with the definitions used in plane geometry (in Book 1) and the second with the definitions used in solid geometry (a.k.a. stereometry) (in Book 11). An important part of the mathematical language still used today has its origin in these 2 sections of definitions. There are also other 2 sections with definitions, about numbers (i.e. natural numbers) and about magnitudes (i.e. non-negative real numbers), which however have been less preserved in the modern terminology.