Thanks for the kind words, and thanks for the very complete understanding of what you are trying to do.

As you know, each locale specifies currency formatting meant to be appropriate to that language and culture. The underlying data doesn’t attempt to provide a global canonical format for anything. So while CLDR data is an amazing resource, it doesn’t satisfy all requirements.

TLDR;

The nearest approximation I think is possible directly is to use the :currency_sumbol option to Money.to_string/2. This option is actually passed to Cldr.Number.to_string/3 and is documented there. I will make sure it is also documented in ex_money. For example:

iex> Money.to_string Money.new(:USD, 100), currency_symbol: :iso, locale: "en"
{:ok, "USD 100.00"}

iex> Money.to_string Money.new(:USD, 100), currency_symbol: :iso, locale: "de"
{:ok, "100,00 USD"}

iex> Money.to_string Money.new(:USD, 100), currency_symbol: :iso, locale: "fr"
{:ok, "100,00 USD"}

This outputs a consistent currency indicator using the ISO 4217 code.

Longer version

In fact you can pass any string you like to the :currency_symbol option but this definitely requires care. Here’s an example using galleons:

iex> Money.to_string Money.new(:USD, 100), currency_symbol: "Galleons", locale: "it"
{:ok, "100,00 Galleons"}

You can identify what format data drives the money - and any other CDLR number - formatting by introspection:

iex> MyApp.Cldr.Number.Format.formats_for "en", :native
{:ok,
 %Cldr.Number.Format{
   accounting: "¤#,##0.00;(¤#,##0.00)",
   currency: "¤#,##0.00",
   currency_long: %{one: [0, " ", 1], other: [0, " ", 1]},
   currency_short: [
     [1000, %{one: ["¤0K", 1], other: ["¤0K", 1]}],
     [10000, %{one: ["¤00K", 2], other: ["¤00K", 2]}],
     [100000, %{one: ["¤000K", 3], other: ["¤000K", 3]}],
     [1000000, %{one: ["¤0M", 1], other: ["¤0M", 1]}],
     [10000000, %{one: ["¤00M", 2], other: ["¤00M", 2]}],
     [100000000, %{one: ["¤000M", 3], other: ["¤000M", 3]}],
     [1000000000, %{one: ["¤0B", 1], other: ["¤0B", 1]}],
     [10000000000, %{one: ["¤00B", 2], other: ["¤00B", 2]}],
     [100000000000, %{one: ["¤000B", 3], other: ["¤000B", 3]}],
     [1000000000000, %{one: ["¤0T", 1], other: ["¤0T", 1]}],
     [10000000000000, %{one: ["¤00T", 2], other: ["¤00T", 2]}],
     [100000000000000, %{one: ["¤000T", 3], other: ["¤000T", 3]}]
   ],
   currency_spacing: %{
     after_currency: %{
       currency_match: "[[:^S:]&[:^Z:]]",
       insert_between: " ",
       surrounding_match: "[[:digit:]]"
     },
     before_currency: %{
       currency_match: "[[:^S:]&[:^Z:]]",
       insert_between: " ",
       surrounding_match: "[[:digit:]]"
     }
   },
   decimal_long: [
     [1000, %{one: ["0 thousand", 1], other: ["0 thousand", 1]}],
     [10000, %{one: ["00 thousand", 2], other: ["00 thousand", 2]}],
     [100000, %{one: ["000 thousand", 3], other: ["000 thousand", 3]}],
     [1000000, %{one: ["0 million", 1], other: ["0 million", 1]}],
     [10000000, %{one: ["00 million", 2], other: ["00 million", 2]}],
     [100000000, %{one: ["000 million", 3], other: ["000 million", 3]}],
     [1000000000, %{one: ["0 billion", 1], other: ["0 billion", 1]}],
     [10000000000, %{one: ["00 billion", 2], other: ["00 billion", 2]}],
     [100000000000, %{one: ["000 billion", 3], other: ["000 billion", 3]}],
     [1000000000000, %{one: ["0 trillion", 1], other: ["0 trillion", 1]}],
     [10000000000000, %{one: ["00 trillion", 2], other: ["00 trillion", 2]}],
     [100000000000000, %{one: ["000 trillion", 3], other: ["000 trillion", 3]}]
   ],
   decimal_short: [
     [1000, %{one: ["0K", 1], other: ["0K", 1]}],
     [10000, %{one: ["00K", 2], other: ["00K", 2]}],
     [100000, %{one: ["000K", 3], other: ["000K", 3]}],
     [1000000, %{one: ["0M", 1], other: ["0M", 1]}],
     [10000000, %{one: ["00M", 2], other: ["00M", 2]}],
     [100000000, %{one: ["000M", 3], other: ["000M", 3]}],
     [1000000000, %{one: ["0B", 1], other: ["0B", 1]}],
     [10000000000, %{one: ["00B", 2], other: ["00B", 2]}],
     [100000000000, %{one: ["000B", 3], other: ["000B", 3]}],
     [1000000000000, %{one: ["0T", 1], other: ["0T", 1]}],
     [10000000000000, %{one: ["00T", 2], other: ["00T", 2]}],
     [100000000000000, %{one: ["000T", 3], other: ["000T", 3]}]
   ],
   other: %{
     approximately: ["~", 0],
     at_least: [0, "+"],
     at_most: ["≤", 0],
     range: [0, "–", 1]
   },
   percent: "#,##0%",
   scientific: "#E0",
   standard: "#,##0.###"
 }}

And use the returned data to make a decision about what format you might want use by introspecting the currency data:

iex> {:ok, currency} = MyApp.Cldr.Currency.currency_for_code :USD, locale: "fr"
{:ok, #Cldr.Currency<"USD">}
iex> currency.
__struct__       alt_code         cash_digits      cash_rounding    
code             count            digits           from             
iso_digits       name             narrow_symbol    rounding         
symbol           tender           to               
iex> currency.symbol
"$US"
iex> currency.narrow_symbol
"$"

Singapore dollar symbols

There is a bug in the CLDR data for the Singapore dollar that should be fixed for CLDR 41 that is currently in “pre alpha” which will probably be release in April. ex_cldr will follow suit on the same day of CLDR release.

Hope this helps, happy to hear any other thoughts, ideas or suggestions!