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6 changes: 5 additions & 1 deletion docs.json
Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,9 @@
"docs/resources/privacy"
]
}
],
"pages": [
"docs/languages/retrieve-supported-languages-for-a-resource"
]
},
{
Expand Down Expand Up @@ -157,7 +160,8 @@
"docs/voice/understanding-voice-sessions",
"docs/voice/message-encoding",
"docs/voice/supported-voice-languages",
"docs/voice/voice-api-requirements"
"docs/voice/voice-api-requirements",
"docs/voice/translate-a-pre-recorded-audio-file"
]
},
{
Expand Down
187 changes: 187 additions & 0 deletions docs/languages/retrieve-supported-languages-for-a-resource.mdx
Original file line number Diff line number Diff line change
@@ -0,0 +1,187 @@
---
title: "Retrieve supported languages for a resource"
description: "Query the Languages API to get the languages and features available for any DeepL resource, so your integration never relies on a hardcoded list."
covers: [Languages]
---

The [`GET /v3/languages`](/api-reference/languages/retrieve-languages-by-resource) endpoint returns the languages supported by a specific DeepL resource, along with which features (formality, glossary, tag handling, and others) each language supports. Use it to populate language dropdowns, validate user input, and toggle feature availability in your integration.

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Intro paragraph covers endpoint behavior well but could hint at the two-endpoint structure earlier

The page covers both GET /v3/languages and GET /v3/languages/resources but the opening paragraph only mentions one endpoint. A reader skimming in 30 seconds may not realize both are covered.

Suggested fix: Add a second sentence to the intro: 'A companion endpoint, GET /v3/languages/resources, describes which side of a language pair (source or target) each feature requires.'

<Info>
For new integrations, use `/v3/languages`. The `/v2/languages` endpoint remains available.
</Info>

You'll need a DeepL API key. Find yours at [deepl.com/your-account/keys](https://www.deepl.com/your-account/keys).

## Fetch languages for a resource

The `resource` parameter is required. It tells the API which DeepL product you're building for, so you get back the right set of languages and features.

Set `resource` to the value that matches your use case — see the [API reference](/api-reference/languages/retrieve-languages-by-resource) for all valid values. This example uses `translate_text` for text translation:

```sh
curl -X GET 'https://api.deepl.com/v3/languages?resource=translate_text' \
--header 'Authorization: DeepL-Auth-Key [yourAuthKey]'
```

```json title="Example response (truncated)"
[
{
"lang": "de",
"name": "German",
"status": "stable",
"usable_as_source": true,
"usable_as_target": true,
"features": {
"formality": { "status": "stable" },
"glossary": { "status": "stable" },
"tag_handling": { "status": "stable" }
}
},
{
"lang": "en",
"name": "English",
"status": "stable",

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Warning box exceeds recommended 1-2 sentence length

The Warning callout on BCP 47 language codes runs to four sentences. CLAUDE.md specifies callout boxes should be 1-2 sentences; longer content should be regular prose.

Suggested fix: Trim to: 'Language codes follow BCP 47 and can include region, script, and variant subtags (e.g. zh-Hans, pt-BR). Treat them as opaque identifiers — do not hardcode assumptions about their format. See Language codes and the release process for details.' Then move the BCP 47 library recommendation into the preceding paragraph as a sentence.

"usable_as_source": true,
"usable_as_target": false,
"features": {
"glossary": { "status": "stable" },
"tag_handling": { "status": "stable" }
}
},
{
"lang": "en-US",
"name": "English (American)",
"status": "stable",
"usable_as_source": false,
"usable_as_target": true,
"features": {
"glossary": { "status": "stable" },
"tag_handling": { "status": "stable" }
}
}
]
```

The response is an array of language objects. See the [API reference](/api-reference/languages/retrieve-languages-by-resource) for the full field list.

<Warning>
Do not hardcode assumptions about language code format. Codes follow BCP 47 and can include region, script, and variant subtags of varying length (e.g. `zh-Hans`, `pt-BR`). Treat them as opaque identifiers and use a BCP 47-compliant library if you need to parse them. See [Language codes and the release process](/docs/resources/language-release-process) for details.
</Warning>

## Filter for valid source and target languages

A language can be usable as a source, a target, both, or neither. Filter on `usable_as_source` and `usable_as_target` depending on what you need. For example, in Python:

```python
import requests

# Fetch once and cache — the language list changes infrequently
resp = requests.get(
"https://api.deepl.com/v3/languages",
params={"resource": "translate_text"},
headers={"Authorization": "DeepL-Auth-Key [yourAuthKey]"},
)
resp.raise_for_status()
languages = resp.json()

# --- Filter by direction ---
source_languages = [l for l in languages if l["usable_as_source"]]
target_languages = [l for l in languages if l["usable_as_target"]]

# --- Check feature availability ---
target = next((l for l in languages if l["lang"] == "de"), None)
supports_formality = target is not None and "formality" in target["features"]
```

Note that `en` (generic English) is usable only as a source, while `en-US` and `en-GB` are usable only as targets. Your language selector for the target field should show the regional variants, not the base code.

## Check feature availability for a language

The `features` object on each language tells you which optional capabilities are available. A feature key is present in `features` only when that language supports it.

To check whether a language supports formality, check for the `formality` key in its `features` object (as shown in the Python example above).

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Second curl example in beta section lacks response diff context

The curl request for include=beta is followed by a truncated response that overlaps heavily with the first response example. The only new information is the Latvian beta entry. The response block could be shortened or annotated to highlight what changed.

Suggested fix: Replace the full response block with a response that shows only the beta-specific entry (Latvian), preceded by a note like 'The response includes the same stable languages as before, plus any beta items. The additional entry looks like:'

Use this pattern to gate UI elements. If `formality` is absent from the target language's `features`, don't offer a formality option in your UI.

Feature `status` values follow the same progression as language `status`: `stable`, `beta`, or `early_access`. By default, the endpoint returns only stable languages and features. To include beta items in the response, add `include=beta` to your query:

```sh
curl -X GET 'https://api.deepl.com/v3/languages?resource=translate_text&include=beta' \
--header 'Authorization: DeepL-Auth-Key [yourAuthKey]'
```

```json title="Example response (truncated)"
[
{
"lang": "de",
"name": "German",
"status": "stable",
"usable_as_source": true,
"usable_as_target": true,
"features": {
"formality": { "status": "stable" },
"glossary": { "status": "stable" },
"tag_handling": { "status": "stable" }
}
},
{
"lang": "lv",
"name": "Latvian",
"status": "beta",
"usable_as_source": true,
"usable_as_target": true,
"features": {
"tag_handling": { "status": "beta" }
}
}
]
```

## Determine which language side a feature requires

Some features require the source language to support them, others require the target, and some require both. To look this up programmatically, call [`GET /v3/languages/resources`](/api-reference/languages/retrieve-language-resources):

```sh
curl -X GET 'https://api.deepl.com/v3/languages/resources' \
--header 'Authorization: DeepL-Auth-Key [yourAuthKey]'
```

```json title="Example response (truncated)"
[
{
"name": "translate_text",
"features": [

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Caching section repeats the 'infrequently' rationale already stated in code comments

The prose in '## Caching the response' restates guidance that inline comments in the Python snippets already communicate ('Fetch once and cache — the language list changes infrequently'). Minor duplication.

Suggested fix: Remove the inline comments from the Python snippets (they now belong to the Caching section as prose) and keep the dedicated section. Or keep the comments and shorten the Caching section to one sentence plus the cross-reference link.

{ "name": "formality", "needs_target_support": true },
{ "name": "glossary", "needs_source_support": true, "needs_target_support": true },
{ "name": "tag_handling", "needs_source_support": true, "needs_target_support": true },
{ "name": "auto_detection", "needs_source_support": true }
]
}
]
```

For the `translate_text` resource, glossary requires both the source and target language to support it. To check whether a specific language pair can use a glossary, use the `languages` list fetched in the example above:

```python
# Reuse the languages list fetched above — do not fetch again
source = next((l for l in languages if l["lang"] == "en"), None)
target = next((l for l in languages if l["lang"] == "de"), None)

supports_glossary = (
source is not None

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Link text in 'What to read next' could be more descriptive for the second item

'Using the Languages API' is slightly ambiguous as link text — it could describe this very page. CLAUDE.md requires descriptive link text.

Suggested fix: Rewrite to: 'See Language resource types and lookup patterns for the full v3 endpoint reference.'

and target is not None
and "glossary" in source["features"]
and "glossary" in target["features"]
)
```

## Caching the response

The language list changes infrequently, only when DeepL adds or updates language support. Cache the response and refresh it on a schedule (daily is sufficient for most integrations) rather than calling the endpoint on every user request.

When DeepL adds a new language, it goes through a staged release. See [Language codes and the release process](/docs/resources/language-release-process) for what to expect and how to write code that handles new codes gracefully.

## What to read next

- [Supported languages](/docs/getting-started/supported-languages) lists every language the DeepL API supports, with feature availability at a glance
- [Using the Languages API](/docs/languages/using-the-languages-api) covers the full v3 endpoint reference and lookup patterns
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