Sheila —

This is following the naming convention of the Septuagint (also known as LXX) Greek translation of the Old Testament. They are transliterated from Greek instead of from Hebrew.

Traditionally, Christians have revered and relied on the Septuagint translation of the Old Testament. Recently, however, more attention, especially by Protestants, has shifted to the so-called "Masoretic Text" (MT) held in custody by the Jews. In the Anglosphere, being mostly Protestant, the MT-derived names of the Old Testament books have gained ascendancy, even in Catholic circles.

The upshot is that, for historical reasons, the names used in these Bibles shifted to a different set of names due to the influence of mostly Protestant biblical scholarship.

Dear Sheila,

I think what you are seeing is a translation evolution since the word originally came from Hebrew but has passed through many different languages.  I believe the Latin vulgate uses “Isaias", so you are likely seeing an English transliteration of that.  

Languages are not static, they are constantly changing, which is why the church chose Latin as the official language of the church.  As a dead language it is no longer subject to the vicissitudes of culture and time.  

Peace,