curl "https://api.phrase.com/v2/projects/:project_id/locales" \
  -u USERNAME_OR_ACCESS_TOKEN \
  -X POST \
  -d '{"branch":"my-feature-branch","name":"de","code":"de-DE","source_locale_id":"abcd1234abcd1234abcd1234abcd1234", "fallback_locale_id":"abcd1234abcd1234abcd1234abcd1234"}' \
  -H 'Content-Type: application/json'

phrase locales create \
--project_id <project_id> \
--data '{"branch":"my-feature-branch", "name":"de", "code":"de-DE", "source_locale_id":"abcd1234abcd1234abcd1234abcd1234", "fallback_locale_id":"abcd1234abcd1234abcd1234abcd1234"}' \
--access_token <token>

import requests

url = "https://api.phrase.com/v2/projects/{project_id}/locales"

payload = {
    "name": "de",
    "code": "de-DE",
    "branch": "my-feature-branch",
    "default": None,
    "main": None,
    "rtl": None,
    "source_locale_id": "abcd1234abcd1234abcd1234abcd1234",
    "fallback_locale_id": "abcd1234abcd1234abcd1234abcd1234",
    "unverify_new_translations": None,
    "unverify_updated_translations": None,
    "autotranslate": None,
    "language_ai_profile": "abcd1234abcd1234abcd1234abcd1234"
}
headers = {
    "Authorization": "<api-key>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    name: 'de',
    code: 'de-DE',
    branch: 'my-feature-branch',
    default: null,
    main: null,
    rtl: null,
    source_locale_id: 'abcd1234abcd1234abcd1234abcd1234',
    fallback_locale_id: 'abcd1234abcd1234abcd1234abcd1234',
    unverify_new_translations: null,
    unverify_updated_translations: null,
    autotranslate: null,
    language_ai_profile: 'abcd1234abcd1234abcd1234abcd1234'
  })
};

fetch('https://api.phrase.com/v2/projects/{project_id}/locales', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.phrase.com/v2/projects/{project_id}/locales",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'name' => 'de',
    'code' => 'de-DE',
    'branch' => 'my-feature-branch',
    'default' => null,
    'main' => null,
    'rtl' => null,
    'source_locale_id' => 'abcd1234abcd1234abcd1234abcd1234',
    'fallback_locale_id' => 'abcd1234abcd1234abcd1234abcd1234',
    'unverify_new_translations' => null,
    'unverify_updated_translations' => null,
    'autotranslate' => null,
    'language_ai_profile' => 'abcd1234abcd1234abcd1234abcd1234'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: <api-key>",
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.phrase.com/v2/projects/{project_id}/locales"

	payload := strings.NewReader("{\n  \"name\": \"de\",\n  \"code\": \"de-DE\",\n  \"branch\": \"my-feature-branch\",\n  \"default\": null,\n  \"main\": null,\n  \"rtl\": null,\n  \"source_locale_id\": \"abcd1234abcd1234abcd1234abcd1234\",\n  \"fallback_locale_id\": \"abcd1234abcd1234abcd1234abcd1234\",\n  \"unverify_new_translations\": null,\n  \"unverify_updated_translations\": null,\n  \"autotranslate\": null,\n  \"language_ai_profile\": \"abcd1234abcd1234abcd1234abcd1234\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "<api-key>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://api.phrase.com/v2/projects/{project_id}/locales")
  .header("Authorization", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"name\": \"de\",\n  \"code\": \"de-DE\",\n  \"branch\": \"my-feature-branch\",\n  \"default\": null,\n  \"main\": null,\n  \"rtl\": null,\n  \"source_locale_id\": \"abcd1234abcd1234abcd1234abcd1234\",\n  \"fallback_locale_id\": \"abcd1234abcd1234abcd1234abcd1234\",\n  \"unverify_new_translations\": null,\n  \"unverify_updated_translations\": null,\n  \"autotranslate\": null,\n  \"language_ai_profile\": \"abcd1234abcd1234abcd1234abcd1234\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.phrase.com/v2/projects/{project_id}/locales")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"name\": \"de\",\n  \"code\": \"de-DE\",\n  \"branch\": \"my-feature-branch\",\n  \"default\": null,\n  \"main\": null,\n  \"rtl\": null,\n  \"source_locale_id\": \"abcd1234abcd1234abcd1234abcd1234\",\n  \"fallback_locale_id\": \"abcd1234abcd1234abcd1234abcd1234\",\n  \"unverify_new_translations\": null,\n  \"unverify_updated_translations\": null,\n  \"autotranslate\": null,\n  \"language_ai_profile\": \"abcd1234abcd1234abcd1234abcd1234\"\n}"

response = http.request(request)
puts response.read_body

{
  "id": "abcd1234cdef1234abcd1234cdef1234",
  "name": "de",
  "code": "de-DE",
  "default": true,
  "main": false,
  "rtl": false,
  "plural_forms": [
    "zero",
    "one",
    "other"
  ],
  "ordinal_plural_forms": [
    "zero",
    "other"
  ],
  "source_locale": {
    "id": "abcd1234cdef1234abcd1234cdef1234",
    "name": "en",
    "code": "en-GB"
  },
  "fallback_locale": {
    "id": "abcd1234cdef1234abcd1234cdef1234",
    "name": "en",
    "code": "en-GB"
  },
  "language_ai_profile": "abcd1234abcd1234abcd1234abcd1234",
  "created_at": "2015-01-28T09:52:53Z",
  "updated_at": "2015-01-28T09:52:53Z",
  "statistics": {
    "keys_total_count": 2120,
    "keys_untranslated_count": 100,
    "words_total_count": 3102102,
    "translations_completed_count": 1920,
    "translations_unverified_count": 32,
    "unverified_words_count": 129,
    "missing_words_count": 3920
  }
}

{
  "message": "Validation Failed",
  "errors": [
    {
      "resource": "Resource",
      "field": "name",
      "message": "can't be blank"
    }
  ]
}