is is really necessary - in english - to say" the day " after tomorrow ? isn't "after tomorrow" sufficient ? i mean, " after tomorrow" cannot mean anything else but ( the day after.... ) but is it really`necessary to say it ? the French say "apres-demain" German says " uebermorgen" Spanish says "pasado manana" - Italian " doppo domani" aso
The day after tomorrow - two days from now.
After tomorrow - two or any larger number of days from now. Certainly, a particular context may take care of this ambiguity, but I would not equate these two expressions.
By the way, in this particular case, I would actually expect the meanings to be different. To me, "I am free after tomorrow" means that the speaker has a very busy day tomorrow, but any other day after that is fine.
Learning English in a Russian course... I would never guess "послезавтра" would need that many words in English... I thought Portuguese was the one weird language that didnt have a name for the day that comes directly after tomorrow... But at least we dont have to say the day because it is obvious.
FYI: Russian "послезавтра" is после+завтра (after tomorrow) merged together. So you would have to ask the same question about Russian: when you just hear the word (so you don't see whether it's one or two words), how do you know what is actually meant? Yet I can't recall a single instance of such a confusion. Personally, I would say "после завтрашнего дня" for "after tomorrow" just to avoid such a confusion, but guess the context often takes care of that as well.
Echoing taffarelbergamin's point, at least Russian Wiktionary seems to mark the stress on the "о" in послезавтра as secondary. I assume that to the ear послезавтра is normally effectively distinct from после завтра, much like "greenhouse" is aurally distinct, because of stress, from "green house" and "bluebird" from "blue bird"?
In Portuguese, the default meaning for "after tomorrow" is the day that comes just after tomorrow because that is usually the meaning you want to express. For saying like "any day after tomorrow" you could say just that, or "any day, except tomorrow" or "any day from the 12th [day of this month, which is the day after tomorrow (bear in mind, we don't say dates in this way. I'm trying to make it closer to English)]".
Usually when you need to express this meaning, the context will help you interpreting it and it rarely becomes ambiguous in a real conversation.
One more case in conversation would be: "No, I can't tomorrow. Only after it". This would express any day after tomorrow, but "No, I can't tomorrow. Only after tomorrow" would imply the day after tomorrow, unless the speaker adds more information.
BTW, we don't really have the word "it" (only he or she, but even then, would not be used in this example). I guess what we would say is more in the lines of "Only after this", but used "it" as it sounds more natural in English.