feat: Supertonic language + total_steps propagation

Language enum expanded from 9 to 33 languages:
- Added 24 new ISO 639-1 languages: AR, BG, CS, DA, DE, EL, ET, FI,
  HR, HU, ID, KO, LT, LV, NL, PL, RO, RU, SK, SL, SV, TR, UK, VI
- Updated display_name, is_cjk (added KO)

Supertonic language mapping (32 languages, no ZH):
- engine.py: _SUPERTONIC_LANG_MAP, engine_language(), supported_languages()
- __init__.py: create_engine() passes config.language to pipeline
- pipeline.py: __init__() accepts language, resolves to ISO code;
  __call__() passes lang= to TTS.synthesize()

total_steps propagation:
- tts_segments(): +total_steps param, conditionally passed to backend
- synthesize_text(): +total_steps param
- run_tts_segment_loop(): +total_steps param
- executor: all 5 synthesize_text() calls pass total_steps

Integration:
- pipeline_factory: create_pipeline_for_job() passes language to supertonic
- preview path: create_pipeline('supertonic', language=language)

Tests updated to accept total_steps in FakeBackend.__call__

plugins/supertonic/__init__.py

@@ -32,11 +32,12 @@ from abogen.tts_plugin.types import EngineConfig
 from .engine import SuperTonicEngine
 
 
-def _load_supertonic_pipeline() -> Any:
+def _load_supertonic_pipeline(language: Any = None) -> Any:
     """Lazy-load SuperTonic dependencies and create pipeline."""
     from plugins.supertonic.pipeline import SupertonicPipeline
 
     return SupertonicPipeline(
+        language=language,
         sample_rate=24000,
         auto_download=True,
         total_steps=5,
@@ -128,7 +129,7 @@ def create_engine(
         EngineError: On failure. Cleans up partially created resources.
     """
     try:
-        pipeline = _load_supertonic_pipeline()
+        pipeline = _load_supertonic_pipeline(language=config.language)
         engine = SuperTonicEngine(pipeline)
         return engine
     except Exception as e:

plugins/supertonic/engine.py

@@ -12,6 +12,7 @@ from typing import Any
 
 import numpy as np
 
+from abogen.domain.enums import Language
 from abogen.tts_plugin.capabilities import VoiceLister
 from abogen.tts_plugin.engine import Engine, EngineSession
 from abogen.tts_plugin.errors import EngineError
@@ -28,6 +29,61 @@ logger = logging.getLogger(__name__)
 # Sample rate for SuperTonic audio
 _SUPERTONIC_SAMPLE_RATE = 24000
 
+# Engine-internal language mapping: Language enum → Supertonic ISO 639-1 code.
+_SUPERTONIC_LANG_MAP: dict[Language, str] = {
+    Language.EN_US: "en",
+    Language.EN_GB: "en",
+    Language.AR: "ar",
+    Language.BG: "bg",
+    Language.CS: "cs",
+    Language.DA: "da",
+    Language.DE: "de",
+    Language.EL: "el",
+    Language.ES: "es",
+    Language.ET: "et",
+    Language.FI: "fi",
+    Language.FR: "fr",
+    Language.HI: "hi",
+    Language.HR: "hr",
+    Language.HU: "hu",
+    Language.ID: "id",
+    Language.IT: "it",
+    Language.JA: "ja",
+    Language.KO: "ko",
+    Language.LT: "lt",
+    Language.LV: "lv",
+    Language.NL: "nl",
+    Language.PL: "pl",
+    Language.PT_BR: "pt",
+    Language.RO: "ro",
+    Language.RU: "ru",
+    Language.SK: "sk",
+    Language.SL: "sl",
+    Language.SV: "sv",
+    Language.TR: "tr",
+    Language.UK: "uk",
+    Language.VI: "vi",
+}
+
+
+def supported_languages() -> list[Language]:
+    """Return the list of Language enum values this engine supports."""
+    return list(_SUPERTONIC_LANG_MAP.keys())
+
+
+def engine_language(lang: Language) -> str:
+    """Map a Language enum to the engine's internal ISO 639-1 code.
+
+    Raises ValueError for unsupported languages.
+    """
+    result = _SUPERTONIC_LANG_MAP.get(lang)
+    if result is None:
+        raise ValueError(
+            f"Supertonic does not support language: {lang!r}. "
+            f"Supported: {supported_languages()}"
+        )
+    return result
+
 
 class SuperTonicSession:
     """EngineSession implementation for SuperTonic.

plugins/supertonic/pipeline.py

@@ -158,6 +158,7 @@ class SupertonicPipeline:
     def __init__(
         self,
         *,
+        language: Any = None,
         sample_rate: int,
         auto_download: bool = True,
         total_steps: int = 5,
@@ -167,6 +168,13 @@ class SupertonicPipeline:
         self.total_steps = int(total_steps)
         self.max_chunk_length = int(max_chunk_length)
 
+        # Resolve language to ISO 639-1 code for Supertonic
+        if language is not None:
+            from plugins.supertonic.engine import engine_language
+            self._lang = engine_language(language)
+        else:
+            self._lang = "en"
+
         _configure_supertonic_gpu()
 
         try:
@@ -212,6 +220,7 @@ class SupertonicPipeline:
                         max_chunk_length=self.max_chunk_length,
                         silence_duration=0.0,
                         verbose=False,
+                        lang=self._lang,
                     )
                     break
                 except ValueError as exc: