Ice to Eskimos in the eastern us. Yes, I know Eskimo isn't preferred but that didn't stop Nana.
Same, or "he could sell igloos to eskimos" to describe an especially skilled salesman.
I've heard "It's like selling ice to Eskimos" used in the context of the OP
Yeah, I've only ever heard it in the "he could sell..." formulation.
Guess we're getting pretty far from the "things to place" idea, but there's always "preaching to the choir"
Carrying water to the sea is the Dutch version.
Seems like that should actually be quite a useful task in the Netherlands considering all the polders!
Of course the Dutch version is about water
Taking guns to America?
What does the phrase mean?
It means to pointlessly take something to a place that already has it in abundance.
Coals to Newcastle works well in Australia too. (I don't think I've ever actually heard that in practice though.)
Same, never heard it used here, and I can't think of any other Australian equivalents.
Bauxite is the obvious one. Bringing bauxite to Australia. How could you forget about bauxite?
Australia also has a Newcastle (in New South Wales, north of Sydney). Not sure if it has/had coal mines, though I wouldn’t be surprised if it did. Australians using the phrase may be referring to their Newcastle, and even unaware of the English one.
Australia also has a Newcastle (in New South Wales, north of Sydney)
Yes, that's why I mentioned it. When I said "works well in Australia", what I meant was "in theory, the same logic you used to apply it to Newcastle-upon-Tyne could be used to apply it to Newcastle, NSW", and not that it actually is used in Australia (I know I've never heard it).
Not sure if it has/had coal mines
Not just does it, but it is in fact home to Australia's largest coal-shipping port. In fact, Port of Newcastle is, according to Wikipedia, the world's largest coal terminal.
Apparently "owls to Athens" is common across Europe? "Wood to the forest" is a variant in the US
It is known in Germany, "Eulen nach Athen tragen". I've heard the explanation that the currency of Athens in antiquity had owl on one side.
Is "Owls to Athens" a reference to Athena?
Yes and no. It's a circular relationship. The proverb is known to have already existed in Ancient Greece. The pantheon (the version that existed before Xerxes torched the place) was apparently inhabited by tons of owls, especially it's roof construction. Since the pantheon was a temple to Athena, people assumed Athena held Owls holy and the owl became linked to Athena, and since Athena was the goddess of wisdom, Owls became a symbol of wisdom. Since the city and her patron goddess are related by name, Athens is linked to owls as well.
But for the meaning: It's to be taken literally. There were many owls in Athens, so they'd not exactly need any more.
Originally it must be, but the animal itself became associated with the city too (for example their coinage almost always had an owl on it)
I don't know. My coworker just said that owls are a symbol of wisdom, and Athens (historically) is the center of wisdom.
I feel like the closest in the deep south is just "preaching to the choir". A redundant task which ignores a probably better path or explaining something to someone who doesn't need it explained to them.
I think "selling ice to Eskimos" is the American equivalent. Naturally, the 
version of this phrase: 1) involves an exonym that's a bit offensive 2) kinda makes doing a pointless exercise sound like a good thing.
Germany:
Regional:
Bringing juggalos to SXSW
Bringing sand to Sahara
We also use "taking coals to Newcastle" here in the Midwestern U.S. (Something about being descended from former British colonies...) But I've heard plenty of riffs on that idea, like, "bringing corn to Iowa."
"Selling sand in sahara."
Taking weed to BC (Canada)
Bring weed to Oregon.
In Poland it is „nosić drewno do lasu” (bring wood to the forest). Similar, but a bit different (pointless not just by being pointless, but by being impossible): „nie zawrócisz kijem Wisły” – 'you won't turn Vistula (our biggest river) with a stick'.
Same in Czech. Nosit dříví do lesa.
For the second one we have "z hovna bič neupleteš" = you can't weave a whip out of a shit.
Taking sand to the beach.
In Spanish we have "llevar leña a la montaña" (take firewood to the mountain) as well as "llevar hierro a Vizcaya" which is take iron to Vizcaya, a city in Spain
When I first heard this phrase, Andy Cole was playing for Newcastle and it was very confusing to me wee mind... Cole's to Newcastle what?
I had to look it up and apparently it's "mencurahkan garam ke laut" a.k.a. "bringing salt to the sea" (Indonesian)
Bringing even more 
flags to :estonia-cool: especially in the last 2 years. The flags and colours are bloody everywhere and not one has been removed.
I'm in the midlands and never heard that phrase but I have heard taking ice to the eskimos, which might be offensive now.
We would say ag tabhairt liúdar go Toraigh (carrying coalfish (pollachius virens) to Tory Island)
Or ag cuimilt saille/blonóige de thóin na muice méithe (rubbing lard on a fat pig's arse)
Ceann amháin eile: cloch go Conamara
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