el: Convert input language

Author: pragmatrix

.github/copilot-instructions.md

@@ -11,3 +11,4 @@
 ## Code Minimalism
 - Avoid defensive code unless there is concrete evidence it is necessary.
 - Avoid redundant logic and repeated calls; keep only the minimal behavior required for correctness.
+- Do not add tests unless explicitly requested by the user.

core/Cargo.toml

@@ -11,4 +11,6 @@ derive_more = { workspace = true }
 
 serde = { workspace = true }
 # For function calling parameters.
-serde_json = { workspace = true }
+serde_json = { workspace = true }
+isolang = "2.4.0"
+oxilangtag = "0.1.5"

core/src/language.rs

@@ -0,0 +1,84 @@
+use std::fmt;
+
+use isolang::Language;
+use oxilangtag::LanguageTag;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum LanguageCodeError {
+    InvalidBcp47Tag { tag: String, message: String },
+    UnsupportedLanguage { language: String },
+}
+
+impl fmt::Display for LanguageCodeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            LanguageCodeError::InvalidBcp47Tag { tag, message } => {
+                write!(f, "Invalid BCP 47 tag '{tag}': {message}")
+            }
+            LanguageCodeError::UnsupportedLanguage { language } => {
+                write!(f, "Unsupported language subtag '{language}'")
+            }
+        }
+    }
+}
+
+impl std::error::Error for LanguageCodeError {}
+
+/// Converts a BCP 47 language tag into its ISO 639-3 language code.
+///
+/// The conversion uses the primary language subtag only and ignores script, region, variant,
+/// and extension subtags.
+pub fn bcp47_to_iso639_3(tag: &str) -> Result<&'static str, LanguageCodeError> {
+    let parsed = LanguageTag::parse(tag).map_err(|error| LanguageCodeError::InvalidBcp47Tag {
+        tag: tag.to_string(),
+        message: error.to_string(),
+    })?;
+
+    let primary_language = parsed.primary_language();
+    let language = match primary_language.len() {
+        2 => Language::from_639_1(primary_language),
+        3 => Language::from_639_3(primary_language),
+        _ => None,
+    };
+
+    language
+        .map(|x| x.to_639_3())
+        .ok_or_else(|| LanguageCodeError::UnsupportedLanguage {
+            language: primary_language.to_string(),
+        })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bcp47_to_iso639_3_for_primary_language_tags() {
+        assert_eq!(bcp47_to_iso639_3("en").unwrap(), "eng");
+        assert_eq!(bcp47_to_iso639_3("de").unwrap(), "deu");
+        assert_eq!(bcp47_to_iso639_3("fr").unwrap(), "fra");
+    }
+
+    #[test]
+    fn bcp47_to_iso639_3_ignores_non_primary_subtags() {
+        assert_eq!(bcp47_to_iso639_3("en-US").unwrap(), "eng");
+        assert_eq!(bcp47_to_iso639_3("zh-Hant-TW").unwrap(), "zho");
+    }
+
+    #[test]
+    fn bcp47_to_iso639_3_rejects_malformed_tags() {
+        let err = bcp47_to_iso639_3("en--US").unwrap_err();
+        assert!(matches!(err, LanguageCodeError::InvalidBcp47Tag { .. }));
+    }
+
+    #[test]
+    fn bcp47_to_iso639_3_rejects_unsupported_primary_language() {
+        let err = bcp47_to_iso639_3("qaa").unwrap_err();
+        assert_eq!(
+            err,
+            LanguageCodeError::UnsupportedLanguage {
+                language: "qaa".to_string(),
+            }
+        );
+    }
+}

core/src/lib.rs

@@ -3,6 +3,7 @@ pub mod billing_collector;
 mod billing_context;
 pub mod conversation;
 mod duration;
+pub mod language;
 mod protocol;
 mod registry;
 pub mod service;

examples/elevenlabs-transcribe.rs

@@ -17,7 +17,7 @@ use context_switch_core::{
     service::Service,
 };
 
-const LANGUAGE: &str = "de";
+const LANGUAGE: &str = "de-DE";
 
 #[tokio::main]
 async fn main() -> Result<()> {

services/elevenlabs/src/transcribe.rs

@@ -21,6 +21,7 @@ use url::Url;
 use context_switch_core::{
     AudioFormat, OutputPath, Service,
     conversation::{Conversation, ConversationInput, ConversationOutput, Input},
+    language::bcp47_to_iso639_3,
 };
 
 const DEFAULT_REALTIME_HOST: &str = "wss://api.elevenlabs.io/v1/speech-to-text/realtime";
@@ -38,7 +39,7 @@ pub struct Params {
     pub model: Option<String>,
     /// Optional websocket endpoint override.
     pub host: Option<String>,
-    /// Optional language hint (ISO 639-1 or ISO 639-3).
+    /// Optional language hint in BCP 47 format (for example `en-US`).
     pub language: Option<String>,
     /// Include detected language in timestamped output.
     /// When omitted, this integration defaults it to `false`.
@@ -262,8 +263,11 @@ fn build_endpoint(params: &Params, audio_encoding: AudioEncoding) -> Result<Url>
         q.append_pair("audio_format", audio_encoding.as_str());
         q.append_pair("commit_strategy", "vad");
 
-        if let Some(language) = &params.language {
-            q.append_pair("language_code", language);
+        if let Some(language) = params.language.as_deref() {
+            let language_code = bcp47_to_iso639_3(language).map_err(|error| {
+                anyhow!("Invalid ElevenLabs params.language '{language}': {error}")
+            })?;
+            q.append_pair("language_code", language_code);
         }
         if let Some(vad_silence_threshold_secs) = params.vad_silence_threshold_secs {
             q.append_pair(