"Explained me" could possibly be used if she is talking about you to someone else and explaining your character or nature to them, but that would be unusual. In English you could just say "She explained the terms" and only include "to me" if you want to emphasize that she explained them to you specifically. But for this particular translation where "me" is included in the Spanish, we need to include "to me" in our translation. Or lose a heart!
In your example, "she explained me" (to the psychiatrist, to the teacher, etc.) "me" is a direct object.-- "me" is what was explained. However, in the Spanish sentence, the direcgt object is "terms", and "me" is an indirect object. Thus, "to me" is needed.
I hear this construction "explain me" instead of "explain to me" frequently from native Spanish speakers who are not yet fluent inEnglish.
Lo siento, pero No., "She explained me the terms" is incorrect (bad) English, and does NOT work. Even lesser educated native speakers do not make that mistake. I don't recall ever hearing it from native speakers, although it is a frequent mistake of native Spanish speaker not fluent in English.
See my explanation above.
I had never heard before either, but now we have. The number of people confused as to why it wasn't accepted proves it to be a regional variation.
And since English doesn't have an equivalent of the RAE or Academie Francais, there's no organization to call a legitimate regional variation "bad English."
Yes the "to" is needed. "She explained the terms to me" is correct. Rearranging the word order requires use of commas and a pause in speech at each comma: "She explained, to me, the terms." Some verbs don't require this such as: "She told me a story." However, explained does. "She explained me the terms" fails to convey the desired clarity. The result would be: "She explained ME..." (then immediately the thought 'What?') before "...the terms" would be heard. The listener would then realize they were talking to a non native speaker and figure out the intended meaning.
"She explained me the terms" is not correct English. She didn't explain me, she explained the terms. Other languages use that phrasing. I've heard many non-native English speakers say "explain me." Who actually can anyone explain (how) another person (is)? Grammatically correct English would properly associate the terms to the explanation: "She explained TO me the terms" or more commonly said, "She explained the terms to me."
All I can say is that in my circles (British English) "explained me the terms" is completely unacceptable.
"She explained to me the terms" does sound a little stilted as a complete sentence, but would not be unusual in a longer sentence, such as "she explained to me the terms that had been agreed by the two governments".
Equally, in a written context, you could express a similar idea as follows. "After telling me that the two governments had reached agreement, she explained to me the terms."
Important point: me in Spanish is the direct object ('me' in English) and also the indirect object ('to me' in English). Occasionally in particular constructions in English we drop the 'to' - eg she told me (IO) the story, he sold me (IO) the car... and in these cases we put the IO before the DO although we can say: she told the story to me, he sold the car to me... In the 60+ years i have spoken/heard English I have never come across this construction with 'explained'. Anyone who has, must have heard a non-native speaker or has such an obscure dialect that it would be absurd for Duo to accept this quirk. repreng btw as so often is correct - "explained to me the terms" is extremely unusual, over-formal or archaic. It might be used in a command but it would be very misleading to let Duo and those learning English think that it is in any way normal.
In English English it is more correct to say "To me she explained the terms." This is, I believe analogous to Spanish "A mi ella explicó los términos." I think most people would actually use the form "She explained the terms to me." The shortened version without the preposition "to" is what you would hear when someone is trying to sound humourously foreign.