Is the lo a necessary part of this sentence. Could it also be "Te he dicho muchas veces."
Your phrase is not correct alone. The "lo" is refering to a sentence, order, words... known by both of them. The verb "decir" in Spanish needs the direct object, you need to put "lo" or to say what you used to tell him. So, your phrase is incomplete.
If so, then my translation "I have told you 'about it' many times." should be correct?
I don't think so. "I have told you about it many times" is something different than "I have told you many times." In the latter, the "lo" (the "it" that the Spanish version refers to) is something that both parties understand to be what they're talking about. I think it's kind of similar to how Spanish speakers say, "Sí, lo sé" ("Yes, I know"), instead of just "Sí, sé" (although I don't think that's necessarily wrong). There's something that is "known," (e.g., where a restaurant is, or how stupid someone is) even though we don't acknowledge it in English with a word of its own (whereas Spanish does).
I don't think so. Told you about it is a neutral phrase, but te lo he dicho muchas veces has a nuance of criticism, like a parent to a child.
'I have told you that many times' is sematically equivalent and sounds better than 'I have told you it many times' Who outside of Appalachia (and perhaps the OK Ozarks) says 'I've told you it'?
Correct solutions: 'I have said it you lots of times.'
Seriously? It wouldn't accept: 'I have said it TO you lots of times.'
DL accepted "I have said it to you many times". Homrul, your word order is a little awkward, but it may also be that DL is not recognizing your contraction "I've". Anyone- I was surprised that no one else had used "said" instead of "told". Isn't said a better translation of decir than told?
I have told you that many times, is better english than I have told you it many times
I have told you IT doesn't sound right. I have told you THAT is what we say. :)