I was checking how to add new units to Cldr following the documentation but I failed.

I added two new units alarm and person, (the settings are listed below).

In iex I tried to get the new alarm unit, but it says it does not exist.
the unit gallon works fine, as in the example.

MyApp.Cldr.Unit.to_string Cldr.Unit.new!(:alarm, 1) 
** (Cldr.UnknownUnitError) Unknown unit was detected at "alarm"
    (ex_cldr_units 3.15.0) lib/cldr/unit.ex:1021: Cldr.Unit.new!/3

Exploring with iex, I manage to see that the new units are there:

iex> Citymonitor.Cldr.Unit.Additional.additional_units
[:alarm, :person]

iex> {:ok, dic_de} = Citymonitor.Cldr.Unit.unit_strings_for :de
iex> dic_de
%{
    {"alarme", [:alarm]},
    {"alarmen", [:alarm]},
    ...
}

iex> {:ok, dic_en} = Citymonitor.Cldr.Unit.unit_strings_for :en
iex> dic_en
%{
    {"al.", [:alarm]},
    {"alarm", [:alarm]},
    ...
}

I was wondering if the custom units should be merged into the core units,
but I don’t know how or where to do this:

Cldr.Unit.known_units() |> merge_base_units()

I would appreciate any hints or tips.

Here is the rest of the configuration.

iex> Citymonitor.Cldr.Unit.Additional.additional_units
[:alarm, :person]

# File: mix.exs 

{:ex_cldr, "~> 2.34"},
{:ex_cldr_numbers, "~> 2.29"},
{:ex_cldr_units, "~> 3.15"},
{:ex_cldr_plugs, "~> 1.2"},
{:ex_cldr_dates_times, "~> 2.13.1"},
...

# File: config/config.exs 

# localization
config :ex_cldr, default_backend: MyApp.Cldr
# ...
# Cldr Units
config :ex_cldr_units,
  default_backend: MyApp.Cldr,
  additional_units: [
    alarm: [base_unit: :unit, factor: 1],
    person: [base_unit: :unit, factor: 1]
  ]

# File:  lib/myapp/cldr/cldr.ex
defmodule Citymonitor.Cldr do
  use Cldr.Unit.Additional

  use Cldr,
    locales: ["en", "de"],
    default_locale: "de",
    fuzzy_threshold: 1,
    gettext: MyApp.Gettext,
    providers: [Cldr.Number, Cldr.Unit, Cldr.List, Cldr.DateTime, Cldr.Calendar]

  # Alarm

  unit_localization(:alarm, "en", :long,
    nominative: %{
      one: "{0} alarm",
      other: "{0} alarm"
    },
    display_name: "alarm"
  )

  unit_localization(:alarm, "en", :short,
    nominative: %{
      one: "{0} al",
      other: "{0} al"
    },
    display_name: "al"
  )

  unit_localization(:alarm, "en", :narrow,
    nominative: %{
      one: "{0} a",
      other: "{0} a"
    },
    display_name: "a"
  )

  unit_localization(:alarm, "de", :long,
    nominative: %{
      one: "{0} Alarme",
      other: "{0} Alarmen"
    },
    display_name: "Alarme"
  )

  unit_localization(:alarm, "de", :short,
    nominative: %{
      one: "{0} Al.",
      other: "{0} Al."
    },
    display_name: "Al."
  )

  unit_localization(:alarm, "de", :narrow,
    nominative: %{
      one: "{0} a",
      other: "{0} a"
    },
    display_name: "a"
  )

  # Person

  unit_localization(:person, "en", :long,
    nominative: %{
      one: "{0} person",
      other: "{0} people"
    },
    display_name: "people"
  )

  unit_localization(:person, "en", :short,
    nominative: %{
      one: "{0} per",
      other: "{0} ppl"
    },
    display_name: "ppl"
  )

  unit_localization(:person, "en", :narrow,
    nominative: %{
      one: "{0} p",
      other: "{0} p"
    },
    display_name: "p"
  )

  unit_localization(:person, "de", :long,
    nominative: %{
      one: "{0} Person",
      other: "{0} Personen"
    },
    display_name: "Personen"
  )

  unit_localization(:person, "de", :short,
    nominative: %{
      one: "{0} Per",
      other: "{0} Prn"
    },
    display_name: "Prn"
  )

  unit_localization(:person, "de", :narrow,
    nominative: %{
      one: "{0} p",
      other: "{0} p"
    },
    display_name: "p"
  )
end