why is "pretérito perfecto" translated as "present perfect"?

Hola James,

Pretérito Perfecto or Pretérito Perfecto Compuesto is the name given to the Present Perfect in English. It is a tense that expresses an action in the past (preterite) but somehow it is seen connected to the present. However in Spanish it is still called Pretérito Perfecto while in English it is called Present Perfect. This is simply the way it goes with grammar in Spanish and grammar in English. 

There are other differences in names in English and Spanish, that simply have to be learned to be honest, and accept that they have different names. For example, in English you have the "present participle" but in Spanish it's not called "presente participio"; we call the -ando/-iendo forms (your -ing form) the "gerund", never el presente participio. 

Here in our site you have a guide to all names given to tenses both in Spain and Latin America, if you want to have a look. I hope it's useful.

Un saludo cordial,

Inma