Maybe we should clarify something here.
A translation of what exactly? What texts do you use to teach beginners?
I have in mind a basic, graded text for beginners. Say, Thrasymachus, Athenaze, Reading Greek, Zuntz’ Griechischer Lehrgang, Rico’s Polis or Beresford & Douglas’s A First Greek Reader or anything similar.
That’s what I teach beginners with, that’s what I learned with. If those are the texts we’re talking about I see absolutely no need whatsoever for a translation. Any competent and patient teacher should be able give a paraphrase or explain via gesticulation, drawings, pictures, synonyms, etc.
I can perfectly see the value of a translation if you’re reading or teaching Thucydides or Lycophron or something on their level. I would perfectly endorse and recommend the use of a translation for pupils who have difficulties with getting a sense of the text, but I would never have a beginner or even an intermediate student read something so complicated without some reasonable help like notes in Greek, a previous explanation and contextualization (in Greek if possible) of what’s going on in the narrative, maps and visual material like pictures of the characters, places and things.
Actually translations are the things I consider less harmful for acquisition. I believe the grammar-centered approach is much more harmful and the teachers that do not actively use the target language to provide comprehensible input (specially basic, everyday vocabulary) are the worst of it all.
This is actually a good argument that I used to believe in until reality hit me in the face… four times, with Thucydides, Nietzsche, Caesar and Machiavelli. These are authors that I revere like divinities and can quote almost from memory (in Spanish) like a devout Christian the Bible, that knowledge served me little for acquisition of the languages when I studied them.
It does undeniably help to understand what the text says, because you already know what’s it all about so can mentally fill the gaps of the words that you don’t understand, but when I tried producing I would almost never remember the vocabulary and grammar constructions these writers use. When doing inverse translation exercises, even if I could recall to memory what Thucydides said, I had a lot of trouble making variations of it, using that vocabulary and constructions to say something different. I see the same effect with my students who know their Plato or Sophocles when they begin to learn Greek. They recognize the passages and have little trouble understanding what it says, but they do not interiorize the grammar and often they give correct interpretations of a given text but cannot explain why their interpretation is correct from a grammar-formal perspective nor can they actively use what they understood to produce correct and meaningful output.
I could perfectly live with it all if it did not had two very adverse effects: it discourages the students who understand the translation and can more or less point to the equivalent Greek but are at a total loss (even when reading the exact same text) without the translation and, most importantly, it easily becomes an addiction, because the teacher has already “normalized” the use of translations the student subconsciously assumes that it is the “normal” process of reading and never gets the courage to read a Greek text without the translation, even when the text is so easy that a translation is not really needed.
Again, I can only picture the case of a self-taught learner where a translation would be helpful at a beginner’s level.