feat(templates): add configurable language tagging rule engine (#58)

docs/OUTPUT_CONFIG.md

@@ -37,7 +37,8 @@ This is **required** in your `unshackle.yaml` — a warning is shown if not conf
 
 Available variables: `{title}`, `{year}`, `{season}`, `{episode}`, `{season_episode}`, `{episode_name}`,
 `{quality}`, `{resolution}`, `{source}`, `{audio}`, `{audio_channels}`, `{audio_full}`,
-`{video}`, `{hdr}`, `{hfr}`, `{atmos}`, `{dual}`, `{multi}`, `{tag}`, `{edition}`, `{repack}`
+`{video}`, `{hdr}`, `{hfr}`, `{atmos}`, `{dual}`, `{multi}`, `{tag}`, `{edition}`, `{repack}`,
+`{lang_tag}`
 
 Add `?` suffix to make a variable conditional (omitted when empty): `{year?}`, `{hdr?}`, `{repack?}`
 
@@ -62,6 +63,72 @@ Example outputs:
 
 ---
 
+---
+
+## language_tags (dict)
+
+Automatically adds language-based identifiers (e.g., `DANiSH`, `NORDiC`, `DKsubs`) to output filenames
+based on audio and subtitle track languages. Use `{lang_tag?}` in your `output_template` to place the tag.
+
+Rules are evaluated in order; the first matching rule wins. All conditions within a single rule
+must match (AND logic). If no rules match, `{lang_tag?}` is cleanly removed from the filename.
+
+### Conditions
+
+| Condition | Type | Description |
+|-----------|------|-------------|
+| `audio` | string | Matches if any selected audio track has this language |
+| `subs_contain` | string | Matches if any selected subtitle has this language |
+| `subs_contain_all` | list | Matches if subtitles include ALL listed languages |
+
+Language matching uses fuzzy matching (e.g., `en` matches `en-US`, `en-GB`).
+
+### Example: Nordic tagging
+
+```yaml
+language_tags:
+  rules:
+    - audio: da
+      tag: DANiSH
+    - audio: sv
+      tag: SWEDiSH
+    - audio: nb
+      tag: NORWEGiAN
+    - audio: en
+      subs_contain_all: [da, sv, nb]
+      tag: NORDiC
+    - audio: en
+      subs_contain: da
+      tag: DKsubs
+
+output_template:
+  movies: '{title}.{year?}.{lang_tag?}.{quality}.{source}.WEB-DL.{audio_full}.{video}-{tag}'
+```
+
+Example outputs:
+- Danish audio: `Show.S01E01.DANiSH.1080p.NF.WEB-DL.DDP5.1.H.264-TAG`
+- English audio + multiple Nordic subs: `Show.S01E01.NORDiC.1080p.NF.WEB-DL.DDP5.1.H.264-TAG`
+- English audio + Danish subs only: `Show.S01E01.DKsubs.1080p.NF.WEB-DL.DDP5.1.H.264-TAG`
+- No matching languages: `Show.S01E01.1080p.NF.WEB-DL.DDP5.1.H.264-TAG`
+
+### Example: Other regional tags
+
+```yaml
+language_tags:
+  rules:
+    - audio: nl
+      tag: DUTCH
+    - audio: de
+      tag: GERMAN
+    - audio: fr
+      subs_contain: en
+      tag: ENGFR
+    - audio: fr
+      tag: FRENCH
+```
+
+---
+
 ## unicode_filenames (bool)
 
 Allow Unicode characters in output filenames. When `false`, Unicode characters are transliterated