I apologize: I wrote this on Wednesday, but I only now noticed that I had not actually posted it (fortunately, it had been saved as a draft). So here it is....
There is, honestly, nothing to worry about. All I mean when I say "idiomatic English" is English following correct grammar and syntax, and in words are used in what could be called a correct way that reflects modern English usage. As I said in yesterday's note, the prime concern when translating is to give an accurate version in English of what the Latin means. Most of the time that will involve paying attention to details of morphology, grammar, and syntax. A nominative noun in the Latin should be kept as a subject if the particular word or English usage allows it. An object in the Latin should stay an object, etc. An active verb in the Latin will usually become an active verb in English. Sometimes English will not allow you to offer a slavishly literal representation of the Latin grammar and syntax and you will have to diverge from the Latin. That is what I mean by idiom.
For example, take the phrase dimisi habenas lacrimis, which I discussed in a post on Monday. In that post I offered several possible English translations, suggesting that "gave free rein to" was the best option: it is the most idiomatic English possibility. We don't normally say "I gave loose rein to my anger," but it is tolerable and understandable English and I would accept it. What we don't say is "I sent away my reins" or the like. Although the Latin verb dimisi can mean that in certain contexts, it is simply wrong to use that English translation in this context. Too many offered "rivers of eyes", omitting "my", or even "rivers of my eyes" for flumina oculorum meorum. To say "rivers of eyes" is wrong. While the genitive case is often represented in English by the preposition "of", it is not always (this use of the genitive is not common; it can be seen as either a type of the genitive used with verbs of plenty [in A&G, #356], suggested by the idea of overflowing in prorumpere [this is related to the partitive genitive]; or an imitation of a common Greek use of the genitive for separation [Greek does not have the ablative case]). In addition, to translate proruperunt as anything but an intransitive verb (which it is in the Latin: it has no object), e.g. "sent forth," would also be wrong. Or consider solitudo mihi ... suggerebatur in line 4 of that passage. "Solitude was suggested to me" is not idiomatic English and would not get full marks, since, simply put, it is not an accurate representation of the meaning of the Latin. Cassell's in this case doesn't offer a suitable synonym, but only the largest dictionaries might (and even then they usually don't). This is an instance where you have to think about what the Latin means and represent it in English. It is not a matter of simply swapping in one particular English word or stem for a Latin word or stem. Of course, we cover such instances in class: I don't expect you to figure them out on your own. And so on....
In short, I am not asking for great English style, ready to be published. I am asking for accurate translations that are in acceptable, correct English. I do not want (for they are ipso facto not accurate) translations that say things in ways that no reasonably capable speaker of English would say.