feat(enrich): fill in the original language from metadata providers

--enrich now sets Title.language when the service left it unset, so video tracks stop falling back to und. Adds original_language to MetadataResult (TMDB, TVDB, OMDb, IMDxAPI) and falls back to OMDb for --imdb, which previously did nothing while imdb_api_enabled defaults to false.

docs/dev/rest-api/endpoints.md

@@ -394,7 +394,7 @@ Create a download job. Requires `service` and `title_id`; every other field is a
 | `tag` | string | `null` | Release group tag. |
 | `tmdb_id` / `imdb_id` / `tvdb_id` / `animeapi_id` | - | `null` | External ID overrides for tagging. |
 | `tvdb_order` | `official`, `dvd`, `absolute`, `alternate`, `regional` | `null` | Renumber episodes to a TVDB season order. Falls back to the `tvdb_order` config option. |
-| `enrich` | boolean | `false` | Override title/year from external source. |
+| `enrich` | boolean | `false` | Override title/year from external source, and fill in the original language. |
 | `output_dir` | string | `null` | Override output directory. |
 | `no_cache` / `reset_cache` | boolean | `false` | Title cache controls. |
 

docs/guide/cli-reference.md

@@ -154,7 +154,7 @@ Keep only certain track types, or skip certain track types. Attachments are alwa
 | `--imdb` | IMDb ID, e.g. `tt1375666`. |
 | `--tvdb` | TVDB ID (integer). Skips the series lookup that `--tvdb-order` would otherwise do. |
 | `--animeapi` | AnimeAPI ID, e.g. `mal:12345` or `anilist:98765` (defaults to MAL). Back-fills TMDB/IMDb/TVDB. |
-| `--enrich` | Override show title/year from the external source. **Requires** one of `--tmdb`, `--imdb`, or `--animeapi`. |
+| `--enrich` | Override show title/year from the external source, and fill in the original language. **Requires** one of `--tmdb`, `--imdb`, or `--animeapi`. |
 | `--tvdb-order` | Renumber episodes to a TVDB season order: `official` (aired), `dvd`, `absolute`, `alternate`, or `regional`. Needs `tvdb_api_key`. |
 
 #### Episode ordering

docs/guide/downloading.md

@@ -583,13 +583,41 @@ tagging and naming:
 | `--imdb` | `--imdb tt1375666` | Use this IMDb ID. |
 | `--tvdb` | `--tvdb 73871` | Use this TVDB ID instead of looking the series up. |
 | `--animeapi` | `--animeapi mal:12345` | Resolve via AnimeAPI (`mal:`/`anilist:` prefix; defaults to MAL). |
-| `--enrich` | - | Override the show title and year from an external source. **Requires** one of `--tmdb`, `--imdb`, or `--animeapi`. |
+| `--enrich` | - | Override the show title and year from an external source, and fill in the original language. **Requires** one of `--tmdb`, `--imdb`, or `--animeapi`. |
 | `--tvdb-order` | `--tvdb-order dvd` | Renumber episodes to a TVDB season order. Needs `tvdb_api_key`. |
 
 ```shell title="Force the right IMDb match and enrich the title"
 unshackle dl --imdb tt1375666 --enrich EXAMPLE 81234567
 ```
 
+### What each metadata provider supplies
+
+Providers differ in what they answer with, so `--enrich` reads different fields depending on
+which ID you gave it. A provider only runs when its key is configured:
+
+| Provider | Config key | Title and year | Original language | External IDs it returns |
+| --- | --- | --- | --- | --- |
+| TMDB | `tmdb_api_key` | yes | yes, alpha-2 such as `ko` | IMDb, TMDB, TVDB |
+| TVDB | `tvdb_api_key` | yes | yes, alpha-3 such as `kor` | TMDB, TVDB, sometimes IMDb |
+| OMDb | `omdb_api_key` | yes | yes, as an English name such as `Korean` | IMDb |
+| IMDxAPI | `imdb_api_enabled` | yes | only when looked up by ID | IMDb |
+| SIMKL | `simkl_client_id` | yes | no, it publishes a country and no language | IMDb, TMDB, TVDB |
+
+Whatever the tag looks like, unshackle normalises it before use, so `ko`, `kor` and `Korean`
+all end up as the same language.
+
+`--enrich` consults these in a fixed order:
+
+- `--tmdb` reads TMDB.
+- `--imdb` tries IMDxAPI, then falls back to OMDb. Since `imdb_api_enabled` is `false` by
+  default, an OMDb key is what makes this path work for most people.
+- `--animeapi` supplies a title only, so pair it with `--tmdb` or `--imdb` if you also want
+  the year and language.
+
+Language is the one field `--enrich` will not overwrite. A service that already reported an
+original language keeps it, because the platform knows its own catalogue better than a
+third-party match does. Everything else follows the usual override behaviour.
+
 ### Episode ordering
 
 A service does not always number a series the way TVDB's aired order does. Some services list

docs/reference/configuration/misc.md

@@ -4,7 +4,9 @@ Smaller configuration areas: external metadata API keys, caching and update chec
 
 ## External API keys { #external-api-keys }
 
-All are unset by default and enable optional metadata/geolocation features.
+All are unset by default and enable optional metadata/geolocation features. For which fields
+each metadata provider can actually answer with, see
+[What each metadata provider supplies](../../guide/downloading.md#what-each-metadata-provider-supplies).
 
 | Key | Type | Default | Description |
 |-----|------|---------|-------------|