# POST Set the default customiser language

Make this language the customiser default: the source every other language is translated from, and the copy the storefront falls back to when a shopper locale has no published language. Exactly one language carries it, so the previous default gives it up in the same transaction. A 422 problem with code `language_not_defaultable` means the language is not eligible: `reason` is `not_published` when it has never been published, or `incomplete_published_translations` when its published copy is missing a required key or has drifted from its source. Publish it first, then retry. Setting the default on the language that already holds it is accepted and changes nothing. The write clears the customiser cached storefront configuration and runs the advisory language sync. It never regenerates your Shopify products, product images, or product cache. An `Idempotency-Key` header is required. Requires the `customisers:write` scope. A 400 problem means the `Idempotency-Key` header is missing or malformed. 401, 403, 404, and 429 problems behave as on the read operation, with `customisers:write` as the required scope.

- Source URL: https://www.signcustomiser.com/help/api/v3-post-set-the-default-customiser-language/
- Markdown URL: https://www.signcustomiser.com/help/api/v3-post-set-the-default-customiser-language.md
- Group: Customiser languages
- Method: POST
- Path: /api/v3/customisers/{customiser_id}/languages/{language_code}/default
- Auth: Bearer token
- Required scopes: `customisers:write`

## Path parameters

- customiser_id (string, required): The customiser id, from the list customisers operation. Example: 1
- language_code (string, required): The language tag, from the list customiser languages operation. Example: fr

## cURL example

```bash
curl https://web.signcustomiser.com/api/v3/customisers/1/languages/fr/default \
  --request POST \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer YOUR_API_TOKEN'
```

## Response examples

### 200 Default language set

```json
{
  "data": {
    "object": "customiser_language",
    "customiser_id": 42,
    "language_code": "fr",
    "source_language_code": "en",
    "display_name": "French",
    "status": "published",
    "is_default": true,
    "translation_summary": {
      "key_count": 184,
      "required_key_count": 96,
      "translated_key_count": 184,
      "retired_key_count": 0,
      "missing_required_key_count": 0,
      "publishable": true
    },
    "ai_translation": null,
    "published_at": "2026-05-04T09:12:31Z",
    "created_at": "2026-05-04T09:09:00Z",
    "updated_at": "2026-05-04T09:14:02Z"
  },
  "links": {
    "self": "https://web.signcustomiser.com/api/v3/customisers/42/languages/fr/default",
    "documentation": "https://www.signcustomiser.com/help/api/"
  },
  "meta": {
    "api_version": "v3",
    "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
  }
}
```

### 403 Insufficient scope

```json
{
  "type": "https://www.signcustomiser.com/help/api/problems/insufficient_scope",
  "title": "Insufficient scope",
  "status": 403,
  "code": "insufficient_scope",
  "detail": "This operation requires the customisers:write scope, but the API key grants the following scopes: customisers:read. Create a key that includes the required scope in the merchant admin under Integrate → API Tokens.",
  "required_scopes": [
    "customisers:write"
  ],
  "granted_scopes": [
    "customisers:read"
  ],
  "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
}
```

### 404 Unknown language

```json
{
  "type": "https://www.signcustomiser.com/help/api/problems/resource_not_found",
  "title": "Resource not found",
  "status": 404,
  "code": "resource_not_found",
  "detail": "The requested resource does not exist or does not belong to the authenticated store.",
  "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
}
```

### 422 Language not published

```json
{
  "type": "https://www.signcustomiser.com/help/api/problems/language_not_defaultable",
  "title": "Language not eligible to be the default",
  "status": 422,
  "code": "language_not_defaultable",
  "detail": "The default language is the source every other language is translated from, so it must be published and carry a current published value for every required key. Publish this language first, then retry.",
  "reason": "not_published",
  "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
}
```