feat(dl): add -fsl/--forced-s-lang to filter forced subtitles by language

docs/dev/rest-api/endpoints.md

@@ -366,6 +366,7 @@ Create a download job. Requires `service` and `title_id`; every other field is a
 | `lang` / `v_lang` / `a_lang` / `s_lang` | string[] | `["orig"]` / `[]` / `[]` / `["all"]` | Language filters. |
 | `require_subs` | string[] | `[]` | Required subtitle languages. |
 | `forced_subs` | boolean | `false` | Include forced subtitles. |
+| `forced_s_lang` | string[] | `[]` | Forced subtitle language(s); implies `forced_subs`. |
 | `exact_lang` | boolean | `false` | Exact language matching. |
 | `sub_format` | string | `null` | Output subtitle format. |
 | `video_only` / `audio_only` / `subs_only` / `chapters_only` | boolean | `false` | Track-type restriction (at most one). |

docs/guide/cli-reference.md

@@ -96,6 +96,7 @@ unshackle dl [OPTIONS] SERVICE [SERVICE ARGS...]
 | `-sl`, `--s-lang` | `all` | Subtitle language(s). |
 | `--require-subs` | - | Required subtitle langs; keeps **all** subs only if these exist. **Cannot combine with `--s-lang`.** |
 | `-fs`, `--forced-subs` | off | Include forced subtitle tracks. |
+| `-fsl`, `--forced-s-lang` | none | Language(s) wanted for forced subtitles; implies `-fs`. |
 | `--exact-lang` | off | Exact matching only: `-l es-419` matches `es-419`, not `es-ES`. |
 | `--sub-format` | - | Output subtitle format (`SRT`/`srt`, `VTT`/`webvtt`, `ASS`/`ssa`, `TTML`, `SMI`, ...), or `original` to keep the source format. |
 

docs/guide/downloading.md

@@ -289,6 +289,9 @@ download on the presence of a specific subtitle track.
 
 - `-fs` / `--forced-subs`: include forced subtitle tracks (signs/foreign dialogue).
   Without this flag, forced subs are dropped from selection.
+- `-fsl` / `--forced-s-lang`: keep forced subtitles only in these languages (implies
+  `-fs`). Works independently of `--s-lang`, so `-sl all -fsl en` grabs every full
+  subtitle but only the English forced track.
 - `--sub-format`: set the output subtitle format, converting only when necessary.
   Accepts codec names/values and common aliases (`srt`, `vtt`, `ass`, `ssa`, `ttml`,
   etc.), or the literal `original` to keep the source format.
@@ -578,6 +581,7 @@ authoritative list.
 | `--v-lang` | `-vl` | Video-only language override. |
 | `--s-lang` | `-sl` | Subtitle language(s); default `all`. |
 | `--forced-subs` | `-fs` | Include forced subtitles. |
+| `--forced-s-lang` | `-fsl` | Forced subtitle language(s); implies `-fs`. |
 | `--sub-format` | | Output subtitle format. |
 | `--wanted` | `-w` | Episode/season range. |
 | `--select-titles` | | Interactively pick episodes or films. |

docs/guide/subtitles.md

@@ -70,6 +70,7 @@ Subtitle selection happens through `dl` flags. The most important is language se
 | `-sl`, `--s-lang` | Language(s) wanted for subtitles. Defaults to `all`. |
 | `--require-subs` | Require these languages to exist; if present, download **all** subtitles. Cannot be combined with `--s-lang`. |
 | `-fs`, `--forced-subs` | Include forced subtitle tracks (excluded by default). |
+| `-fsl`, `--forced-s-lang` | Language(s) wanted for forced subtitles; implies `-fs`. |
 | `--exact-lang` | Exact language matching, with no regional variants. |
 | `-S`, `--subs-only` | Download only subtitle tracks. |
 | `-ns`, `--no-subs` | Do not download subtitle tracks at all. |
@@ -121,6 +122,18 @@ default**. Add `-fs` / `--forced-subs` to include them:
 unshackle dl --s-lang en --forced-subs EXAMPLE 81234567
 ```
 
+`-fs` keeps forced tracks in every selected language. If you only want forced tracks
+in certain languages, use `-fsl` / `--forced-s-lang` instead. It implies `-fs`, so
+you do not need both:
+
+```shell title="All full subtitles, but only the English forced track"
+unshackle dl --s-lang all --forced-s-lang en EXAMPLE 81234567
+```
+
+If you pass both flags, `-fsl` wins and keeps only forced tracks in its languages.
+It also understands `orig` (the title's original language) and `all` (every forced
+track, same as plain `-fs`).
+
 ## Track types: forced, SDH, and CC
 
 Every subtitle track carries flags describing what kind of captions it holds. These

docs/reference/configuration.md

@@ -320,6 +320,7 @@ Common keys (a useful subset; every `dl` flag works):
 | `channels` | float | *(unset)* | Audio channels, e.g. `6` for 5.1. |
 | `sub_format` | str | *(unset)* | Convert subtitles to this format (`srt`, `vtt`, `original`, ...). |
 | `forced_subs` | bool | `false` | Include forced subtitle tracks. |
+| `forced_s_lang` | list | `[]` | Forced subtitle language(s); implies `forced_subs`. |
 | `no_subs` / `no_audio` / `no_chapters` | bool | `false` | Skip that track type. |
 | `downloads` | int | `1` | Tracks downloaded concurrently. |
 | `workers` | int | *(downloader default)* | Threads per track. |