diff --git a/abogen/application/conversion_executor.py b/abogen/application/conversion_executor.py
index 372f7bc..a866268 100644
--- a/abogen/application/conversion_executor.py
+++ b/abogen/application/conversion_executor.py
@@ -277,6 +277,7 @@ def execute_conversion(
                 backend=intro_backend,
                 voice=intro_voice,
                 speed=intro_speed or request.speed,
+                total_steps=intro_steps,
                 chapter_sink=None,
                 preview_callback=lambda text: events.log(f"  {text[:80]}"),
             )
@@ -347,6 +348,7 @@ def execute_conversion(
                     backend=intro_backend,
                     voice=intro_voice,
                     speed=intro_speed or request.speed,
+                    total_steps=intro_steps,
                     chapter_sink=chapter_sink,
                     preview_callback=lambda text: events.log(f"  Intro: {text[:80]}"),
                 )
@@ -421,6 +423,7 @@ def execute_conversion(
                     seg_provider = chapter_provider
                     seg_voice = chapter_voice
                     seg_speed = chapter_speed
+                    seg_steps = chapter_steps
                     seg_backend = chapter_backend
 
                 # Track voice for chapter marker
@@ -452,6 +455,7 @@ def execute_conversion(
                         backend=seg_backend,
                         voice=seg_voice,
                         speed=seg_speed or request.speed,
+                        total_steps=seg_steps,
                         chapter_sink=chapter_sink,
                         preview_callback=lambda text: events.log(f"  {text[:80]}"),
                         split_pattern_override=active_split,
@@ -539,6 +543,7 @@ def execute_conversion(
                 backend=outro_backend,
                 voice=outro_voice,
                 speed=outro_speed or request.speed,
+                total_steps=outro_steps,
                 chapter_sink=None,
                 preview_callback=lambda text: events.log(f"  {text[:80]}"),
             )
diff --git a/abogen/domain/conversion_engine.py b/abogen/domain/conversion_engine.py
index c21b80f..21fd1ed 100644
--- a/abogen/domain/conversion_engine.py
+++ b/abogen/domain/conversion_engine.py
@@ -61,6 +61,7 @@ def run_tts_segment_loop(
     voice: Any,
     speed: float,
     split_pattern: str,
+    total_steps: Optional[int] = None,
     chapter_sink: Optional[AudioSink] = None,
     preview_callback: Optional[Callable[[str], None]] = None,
     on_segment: Optional[Callable[[SegmentInfo], None]] = None,
@@ -74,6 +75,7 @@ def run_tts_segment_loop(
         voice: Voice name/id for the backend.
         speed: Speech speed multiplier.
         split_pattern: Regex pattern used by the TTS engine for sentence splitting.
+        total_steps: Inference quality steps (Supertonic only, ignored by Kokoro).
         preview_callback: Called with a short preview string per segment.
         on_segment: Called with a SegmentInfo for each segment *before*
             audio is written.  Useful for callers that need per-segment
@@ -95,6 +97,7 @@ def run_tts_segment_loop(
         speed=speed,
         split_pattern=split_pattern,
         current_time=params.stats.current_time,
+        total_steps=total_steps,
     ):
         if params.check_cancel():
             break
@@ -212,6 +215,7 @@ def synthesize_text(
     backend: Any,
     voice: Any,
     speed: float,
+    total_steps: Optional[int] = None,
     chapter_sink: Optional[AudioSink] = None,
     preview_callback: Optional[Callable[[str], None]] = None,
     on_segment: Optional[Callable[[SegmentInfo], None]] = None,
@@ -229,6 +233,7 @@ def synthesize_text(
         backend=backend,
         voice=voice,
         speed=speed,
+        total_steps=total_steps,
         split_pattern=split_pattern_override or params.tts_context.split_pattern,
         chapter_sink=chapter_sink,
         preview_callback=preview_callback,
diff --git a/abogen/domain/conversion_pipeline.py b/abogen/domain/conversion_pipeline.py
index a383c5f..9afbf45 100644
--- a/abogen/domain/conversion_pipeline.py
+++ b/abogen/domain/conversion_pipeline.py
@@ -146,6 +146,7 @@ def tts_segments(
     speed: float,
     split_pattern: str,
     current_time: float = 0.0,
+    total_steps: Optional[int] = None,
 ) -> Iterator[SegmentResult]:
     """Invoke TTS backend on (already normalized) text and yield SegmentResults.
 
@@ -159,16 +160,20 @@ def tts_segments(
         speed: TTS speed multiplier.
         split_pattern: Regex pattern for sentence splitting.
         current_time: Current position in the audio timeline (seconds).
+        total_steps: Inference quality steps (Supertonic only, ignored by Kokoro).
 
     Yields:
         SegmentResult for each non-empty TTS segment.
     """
-    segment_iter = backend(
-        text,
+    kwargs: dict[str, Any] = dict(
         voice=voice,
         speed=speed,
         split_pattern=split_pattern,
     )
+    if total_steps is not None:
+        kwargs["total_steps"] = total_steps
+
+    segment_iter = backend(text, **kwargs)
 
     chunk_start = current_time
 
@@ -215,6 +220,7 @@ def emit_text_segments(
     speed: float,
     split_pattern: str,
     current_time: float = 0.0,
+    total_steps: Optional[int] = None,
     # normalization
     heteronym_rules: Any = None,
     pronunciation_rules: Any = None,
@@ -265,6 +271,7 @@ def emit_text_segments(
         speed=speed,
         split_pattern=split_pattern,
         current_time=current_time,
+        total_steps=total_steps,
     )
 
 
diff --git a/abogen/domain/enums.py b/abogen/domain/enums.py
index 8bc74c6..bdf0abf 100644
--- a/abogen/domain/enums.py
+++ b/abogen/domain/enums.py
@@ -128,8 +128,8 @@ class InputFormat(str, Enum):
 class Language(str, Enum):
     """TTS language code (ISO 639-1 with region where needed).
 
-    Each engine (Kokoro, Supertonic) maps these to its own
-    internal language identifiers.
+    Each engine maps these to its own internal language identifiers.
+    Engines report which languages they support via ``supported_languages()``.
     """
     EN_US = "en-US"
     EN_GB = "en-GB"
@@ -140,6 +140,30 @@ class Language(str, Enum):
     JA = "ja"
     PT_BR = "pt-BR"
     ZH = "zh"
+    AR = "ar"
+    BG = "bg"
+    CS = "cs"
+    DA = "da"
+    DE = "de"
+    EL = "el"
+    ET = "et"
+    FI = "fi"
+    HR = "hr"
+    HU = "hu"
+    ID = "id"
+    KO = "ko"
+    LT = "lt"
+    LV = "lv"
+    NL = "nl"
+    PL = "pl"
+    RO = "ro"
+    RU = "ru"
+    SK = "sk"
+    SL = "sl"
+    SV = "sv"
+    TR = "tr"
+    UK = "uk"
+    VI = "vi"
 
     @property
     def display_name(self) -> str:
@@ -154,13 +178,37 @@ class Language(str, Enum):
             "ja": "Japanese",
             "pt-BR": "Brazilian Portuguese",
             "zh": "Mandarin Chinese",
+            "ar": "Arabic",
+            "bg": "Bulgarian",
+            "cs": "Czech",
+            "da": "Danish",
+            "de": "German",
+            "el": "Greek",
+            "et": "Estonian",
+            "fi": "Finnish",
+            "hr": "Croatian",
+            "hu": "Hungarian",
+            "id": "Indonesian",
+            "ko": "Korean",
+            "lt": "Lithuanian",
+            "lv": "Latvian",
+            "nl": "Dutch",
+            "pl": "Polish",
+            "ro": "Romanian",
+            "ru": "Russian",
+            "sk": "Slovak",
+            "sl": "Slovenian",
+            "sv": "Swedish",
+            "tr": "Turkish",
+            "uk": "Ukrainian",
+            "vi": "Vietnamese",
         }
         return _names[self.value]
 
     @property
     def is_cjk(self) -> bool:
-        """True for CJK languages (Chinese, Japanese)."""
-        return self in (self.ZH, self.JA)
+        """True for CJK languages (Chinese, Japanese, Korean)."""
+        return self in (self.ZH, self.JA, self.KO)
 
     @property
     def supports_subtitle_tokens(self) -> bool:
diff --git a/abogen/domain/pipeline_factory.py b/abogen/domain/pipeline_factory.py
index 84c7c8c..74cb37d 100644
--- a/abogen/domain/pipeline_factory.py
+++ b/abogen/domain/pipeline_factory.py
@@ -45,7 +45,7 @@ def create_pipeline_for_job(
         provider = "kokoro"
 
     if provider == "supertonic":
-        return create_pipeline("supertonic")
+        return create_pipeline("supertonic", language=language)
 
     device = resolve_device(use_gpu)
     return create_pipeline("kokoro", language=language, device=device)
diff --git a/abogen/webui/routes/utils/synthesize.py b/abogen/webui/routes/utils/synthesize.py
index 92c87f2..8702157 100644
--- a/abogen/webui/routes/utils/synthesize.py
+++ b/abogen/webui/routes/utils/synthesize.py
@@ -116,7 +116,7 @@ def generate_preview_audio(
     if provider == "supertonic":
         from abogen.tts_plugin.utils import create_pipeline
 
-        pipeline = create_pipeline("supertonic")
+        pipeline = create_pipeline("supertonic", language=language)
         segments = pipeline(
             normalized_text,
             voice=voice_spec,
diff --git a/plugins/supertonic/__init__.py b/plugins/supertonic/__init__.py
index d6eeac4..1a34906 100644
--- a/plugins/supertonic/__init__.py
+++ b/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:
diff --git a/plugins/supertonic/engine.py b/plugins/supertonic/engine.py
index 70dca6c..e95e3bc 100644
--- a/plugins/supertonic/engine.py
+++ b/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.
diff --git a/plugins/supertonic/pipeline.py b/plugins/supertonic/pipeline.py
index aabf3d7..6bccf67 100644
--- a/plugins/supertonic/pipeline.py
+++ b/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:
diff --git a/tests/test_application_coverage.py b/tests/test_application_coverage.py
index d044aa8..fa047d2 100644
--- a/tests/test_application_coverage.py
+++ b/tests/test_application_coverage.py
@@ -54,7 +54,7 @@ class FakeBackend:
     def __init__(self):
         self.synthesized: List[str] = []
 
-    def __call__(self, text: str, *, voice: Any, speed: float = 1.0, split_pattern: str = "") -> List:
+    def __call__(self, text: str, *, voice: Any, speed: float = 1.0, split_pattern: str = "", **kwargs: Any) -> List:
         self.synthesized.append(text)
 
         class FakeSegment:
diff --git a/tests/test_conversion_executor.py b/tests/test_conversion_executor.py
index 75bfb74..42bd9e9 100644
--- a/tests/test_conversion_executor.py
+++ b/tests/test_conversion_executor.py
@@ -58,7 +58,7 @@ class FakeBackend:
         self.segment_duration = segment_duration
         self.call_count = 0
 
-    def __call__(self, text: str, voice: Any, speed: float = 1.0, split_pattern: str = ""):
+    def __call__(self, text: str, voice: Any, speed: float = 1.0, split_pattern: str = "", **kwargs: Any):
         self.call_count += 1
         # Return fake segment objects with required attributes
         @dataclass
diff --git a/tests/test_conversion_executor_unified.py b/tests/test_conversion_executor_unified.py
index 359f5bb..b700312 100644
--- a/tests/test_conversion_executor_unified.py
+++ b/tests/test_conversion_executor_unified.py
@@ -73,7 +73,7 @@ class FakeBackend:
     def __init__(self):
         self.synthesized: List[str] = []
 
-    def __call__(self, text: str, *, voice: Any, speed: float = 1.0, split_pattern: str = "") -> List:
+    def __call__(self, text: str, *, voice: Any, speed: float = 1.0, split_pattern: str = "", **kwargs: Any) -> List:
         """Return fake TTS segments."""
         self.synthesized.append(text)
 
diff --git a/tests/test_domain_pipeline_factory.py b/tests/test_domain_pipeline_factory.py
index f0a27cb..80006c3 100644
--- a/tests/test_domain_pipeline_factory.py
+++ b/tests/test_domain_pipeline_factory.py
@@ -33,7 +33,7 @@ class TestCreatePipelineForJob:
     def test_supertonic_provider(self, _reg, mock_create):
         mock_create.return_value = MagicMock()
         result = create_pipeline_for_job("supertonic", Language.EN_US, use_gpu=True)
-        mock_create.assert_called_once_with("supertonic")
+        mock_create.assert_called_once_with("supertonic", language=Language.EN_US)
         assert result is mock_create.return_value
 
     @patch("abogen.domain.pipeline_factory.create_pipeline")
diff --git a/tests/test_kokoro_plugin.py b/tests/test_kokoro_plugin.py
index fa86776..a73f800 100644
--- a/tests/test_kokoro_plugin.py
+++ b/tests/test_kokoro_plugin.py
@@ -49,7 +49,7 @@ def _make_mock_engine() -> Any:
     from plugins.kokoro.engine import KokoroEngine
 
     class MockPipeline:
-        def __call__(self, text, voice, speed, split_pattern=None):
+        def __call__(self, text, voice, speed, split_pattern=None, **kwargs):
             class MockSegment:
                 def __init__(self):
                     self.audio = MockAudio()