The title of the translation is wrong. Anyone who wrote (or writes) in Latin is well aware that the ending -orum is genitive plural, not singular. Clearly, therefore, Euler did mean his book title to read 'Introduction to the Analysis of Infinities.' In effect, the translator says that he changed this, because it doesn't accord with modern mathematics. That is, the plural term 'infinities' is archaic. All current mathematicians (who have looked into the matter) accept that not all infinities are the same size. The implication of this is that there exists more than one 'infinity' (if we're going to talk about 'infinity'). Mathematics are similar in all languages, so the book is still decent (though not as good as it could be).