diff --git a/changelog/4045.fixed.md b/changelog/4045.fixed.md
new file mode 100644
index 000000000..ecae78969
--- /dev/null
+++ b/changelog/4045.fixed.md
@@ -0,0 +1 @@
+Fixed `SonioxSTTService` crash when `language_hints` contains plain strings instead of `Language` enum values.
diff --git a/src/pipecat/services/soniox/stt.py b/src/pipecat/services/soniox/stt.py
index f123d850c..5163ef113 100644
--- a/src/pipecat/services/soniox/stt.py
+++ b/src/pipecat/services/soniox/stt.py
@@ -27,7 +27,7 @@ from pipecat.processors.frame_processor import FrameDirection
 from pipecat.services.settings import NOT_GIVEN, STTSettings, _NotGiven
 from pipecat.services.stt_latency import SONIOX_TTFS_P99
 from pipecat.services.stt_service import WebsocketSTTService
-from pipecat.transcriptions.language import Language
+from pipecat.transcriptions.language import Language, resolve_language
 from pipecat.utils.time import time_now_iso8601
 from pipecat.utils.tracing.service_decorators import traced_stt
 
@@ -118,14 +118,75 @@ def is_end_token(token: dict) -> bool:
 
 
 def language_to_soniox_language(language: Language) -> str:
-    """Pipecat Language enum uses same ISO 2-letter codes as Soniox, except with added regional variants.
+    """Convert a Pipecat Language to a Soniox language code.
 
-    For a list of all supported languages, see: https://soniox.com/docs/speech-to-text/core-concepts/supported-languages
+    For a list of all supported languages, see:
+    https://soniox.com/docs/speech-to-text/core-concepts/supported-languages
     """
-    lang_str = str(language.value).lower()
-    if "-" in lang_str:
-        return lang_str.split("-")[0]
-    return lang_str
+    LANGUAGE_MAP = {
+        Language.AF: "af",
+        Language.AR: "ar",
+        Language.AZ: "az",
+        Language.BE: "be",
+        Language.BG: "bg",
+        Language.BN: "bn",
+        Language.BS: "bs",
+        Language.CA: "ca",
+        Language.CS: "cs",
+        Language.CY: "cy",
+        Language.DA: "da",
+        Language.DE: "de",
+        Language.EL: "el",
+        Language.EN: "en",
+        Language.ES: "es",
+        Language.ET: "et",
+        Language.EU: "eu",
+        Language.FA: "fa",
+        Language.FI: "fi",
+        Language.FR: "fr",
+        Language.GL: "gl",
+        Language.GU: "gu",
+        Language.HE: "he",
+        Language.HI: "hi",
+        Language.HR: "hr",
+        Language.HU: "hu",
+        Language.ID: "id",
+        Language.IT: "it",
+        Language.JA: "ja",
+        Language.KA: "ka",
+        Language.KK: "kk",
+        Language.KN: "kn",
+        Language.KO: "ko",
+        Language.LT: "lt",
+        Language.LV: "lv",
+        Language.MK: "mk",
+        Language.ML: "ml",
+        Language.MR: "mr",
+        Language.MS: "ms",
+        Language.NL: "nl",
+        Language.NO: "no",
+        Language.PA: "pa",
+        Language.PL: "pl",
+        Language.PT: "pt",
+        Language.RO: "ro",
+        Language.RU: "ru",
+        Language.SK: "sk",
+        Language.SL: "sl",
+        Language.SQ: "sq",
+        Language.SR: "sr",
+        Language.SV: "sv",
+        Language.SW: "sw",
+        Language.TA: "ta",
+        Language.TE: "te",
+        Language.TH: "th",
+        Language.TL: "tl",
+        Language.TR: "tr",
+        Language.UK: "uk",
+        Language.UR: "ur",
+        Language.VI: "vi",
+        Language.ZH: "zh",
+    }
+    return resolve_language(language, LANGUAGE_MAP, use_base_code=True)
 
 
 def _prepare_language_hints(
diff --git a/src/pipecat/transcriptions/language.py b/src/pipecat/transcriptions/language.py
index a79a85166..1980590e3 100644
--- a/src/pipecat/transcriptions/language.py
+++ b/src/pipecat/transcriptions/language.py
@@ -631,13 +631,13 @@ def resolve_language(
         return result
 
     # Not in map - fall back with warning
-    lang_str = str(language.value)
+    lang_str = str(language)
 
     if use_base_code:
         # Extract base code (e.g., "en" from "en-US")
         base_code = lang_str.split("-")[0].lower()
-        logger.warning(f"Language {language.value} not verified. Using base code '{base_code}'.")
+        logger.warning(f"Language {language} not verified. Using base code '{base_code}'.")
         return base_code
     else:
-        logger.warning(f"Language {language.value} not verified. Using '{lang_str}'.")
+        logger.warning(f"Language {language} not verified. Using '{lang_str}'.")
         return lang_str