diff --git a/abogen/constants.py b/abogen/constants.py
index b45d4da..95b28eb 100644
--- a/abogen/constants.py
+++ b/abogen/constants.py
@@ -70,11 +70,12 @@ SUPPORTED_INPUT_FORMATS = [
     "vtt",
 ]
 
-# Supported languages for subtitle generation
-# Currently, only English (EN_US, EN_GB) are supported for subtitle generation.
-# This is because tokens that contain timestamps are not generated for other languages in the Kokoro pipeline.
-# Please refer to: https://github.com/hexgrad/kokoro/blob/6d87f4ae7abc2d14dbc4b3ef2e5f19852e861ac2/kokoro/pipeline.py
-SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION = [Language.EN_US, Language.EN_GB]
+# Supported languages for subtitle generation.
+# All languages are supported: only English emits per-word timestamped tokens
+# in the Kokoro pipeline, but other languages fall back to segment-level fake
+# tokens (see abogen.domain.tokens.FakeToken), so subtitles are still
+# generated at segment granularity.
+SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION = list(Language)
 
 # Voice and sample text mapping
 SAMPLE_VOICE_TEXTS = {
diff --git a/abogen/domain/conversion_pipeline.py b/abogen/domain/conversion_pipeline.py
index 9afbf45..ad4e56f 100644
--- a/abogen/domain/conversion_pipeline.py
+++ b/abogen/domain/conversion_pipeline.py
@@ -112,12 +112,10 @@ def spacy_pre_tts_segmentation(
 
 
 def _to_language_enum(lang_code: Any) -> Language:
-    """Convert lang_code to Language enum."""
-    if isinstance(lang_code, Language):
-        return lang_code
+    """Convert lang_code to Language enum (ISO code or Language enum)."""
     try:
         return Language.from_str(str(lang_code))
-    except (ValueError, AttributeError):
+    except ValueError:
         return Language.EN_US
 
 
diff --git a/abogen/domain/enums.py b/abogen/domain/enums.py
index bdf0abf..40f304d 100644
--- a/abogen/domain/enums.py
+++ b/abogen/domain/enums.py
@@ -212,8 +212,12 @@ class Language(str, Enum):
 
     @property
     def supports_subtitle_tokens(self) -> bool:
-        """True if this language generates timestamped tokens for subtitles."""
-        return self in (self.EN_US, self.EN_GB)
+        """True if this language supports subtitle generation.
+
+        All languages are supported: languages without per-word timestamped
+        tokens fall back to segment-level fake tokens in the pipeline.
+        """
+        return True
 
     @classmethod
     def from_str(cls, value: str) -> Language:
diff --git a/abogen/domain/split_pattern.py b/abogen/domain/split_pattern.py
index 01daf9d..616d918 100644
--- a/abogen/domain/split_pattern.py
+++ b/abogen/domain/split_pattern.py
@@ -16,7 +16,7 @@ def get_split_pattern(language: Language, subtitle_mode: str) -> str:
     """Get the appropriate split pattern based on language and subtitle mode.
 
     Args:
-        language: Language enum value.
+        language: Language enum value, ISO code, or kokoro letter code.
         subtitle_mode: Subtitle mode ("Sentence", "Sentence + Comma", "Line", etc.)
 
     Returns:
diff --git a/abogen/pyqt/conversion.py b/abogen/pyqt/conversion.py
index 3787c0a..ff3a829 100644
--- a/abogen/pyqt/conversion.py
+++ b/abogen/pyqt/conversion.py
@@ -22,6 +22,7 @@ from abogen.constants import (
 )
 from abogen.infrastructure.subtitle_writer import make_subtitle_writer, resolve_subtitle_format
 from abogen.domain.split_pattern import get_split_pattern
+from abogen.domain.enums import Language
 from abogen.domain.subtitle_processor import (
     parse_subtitle_file,
     process_subtitle_entries,
@@ -872,12 +873,12 @@ class ConversionThread(QThread):
                     )
                     spacy_sentences = None
                     active_split_pattern = self.split_pattern
-                    spacing_pattern = r"\s*" if self.lang_code in ["z", "j"] else r"\s+"
+                    spacing_pattern = r"\s*" if self.lang_code in (Language.JA, Language.ZH) else r"\s+"
 
                     # Pre-load spaCy model for English if it will be needed for subtitle generation
                     if (
                         use_spacy
-                        and self.lang_code in ["a", "b"]
+                        and self.lang_code in (Language.EN_US, Language.EN_GB)
                         and self.subtitle_mode in ["Sentence", "Sentence + Comma"]
                     ):
                         from abogen.spacy_utils import get_spacy_model
@@ -894,7 +895,7 @@ class ConversionThread(QThread):
                                 )
                             )
 
-                    if use_spacy and self.lang_code not in ["a", "b"]:
+                    if use_spacy and self.lang_code not in (Language.EN_US, Language.EN_GB):
                         # Non-English: use spaCy for pre-TTS segmentation
                         self.log_updated.emit(
                             ("\nUsing spaCy for sentence segmentation (pre-TTS)...", "grey")
@@ -1011,7 +1012,7 @@ class ConversionThread(QThread):
                             audio_sink=merged_sink if merge_chapters_at_end else None,
                             subtitle_mode=self.subtitle_mode,
                             max_subtitle_words=self.max_subtitle_words,
-                            lang_code=self.lang_code,
+                            language=self.lang_code,
                             use_spacy_segmentation=getattr(self, "use_spacy_segmentation", False),
                         )
 
diff --git a/abogen/pyqt/gui.py b/abogen/pyqt/gui.py
index 6f33d2d..9ed5bc7 100644
--- a/abogen/pyqt/gui.py
+++ b/abogen/pyqt/gui.py
@@ -75,6 +75,7 @@ from abogen.domain.text_utils import calculate_text_length
 
 from abogen.pyqt.conversion import ConversionThread, VoicePreviewThread, PlayAudioThread, ChapterOptionsDialog, TimestampDetectionDialog
 from abogen.pyqt.book_handler import HandlerDialog
+from abogen.domain.enums import Language
 from abogen.constants import (
     PROGRAM_NAME,
     VERSION,
@@ -88,8 +89,9 @@ from abogen.constants import (
 from abogen.tts_plugin.utils import get_voices
 import threading
 from abogen.pyqt.voice_formula_gui import VoiceFormulaDialog
-from abogen.voice_profiles import load_profiles
+from abogen.voice_profiles import load_profiles, resolve_profile_language
 from abogen.domain.settings_core import all_settings_defaults
+from plugins.kokoro.engine import language_for_code, language_for_voice_id
 
 # Module-level default cache for use outside __init__
 _DEFAULTS = all_settings_defaults()
@@ -397,11 +399,7 @@ class InputBox(QLabel):
         # Re-enable subtitle and replace newlines controls when cleared
         window = self.window()
         if hasattr(window, "subtitle_combo"):
-            # Only enable if language supports it
-            current_lang = getattr(window, "selected_lang", "a")
-            window.subtitle_combo.setEnabled(
-                current_lang in SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION
-            )
+            window.subtitle_combo.setEnabled(True)
         if hasattr(window, "replace_newlines_combo"):
             window.replace_newlines_combo.setEnabled(True)
 
@@ -941,7 +939,7 @@ class abogen(QWidget):
             self.selected_lang = None
         else:
             self.selected_voice = self.config.get("selected_voice", _d["selected_voice"])
-            self.selected_lang = self.selected_voice[0] if self.selected_voice else None
+            self.selected_lang = language_for_voice_id(self.selected_voice)
         self.is_converting = False
         self.subtitle_mode = self.config.get("subtitle_mode", _d["subtitle_mode"])
         self.max_subtitle_words = self.config.get("max_subtitle_words", _d["max_subtitle_words"])
@@ -1012,10 +1010,12 @@ class abogen(QWidget):
                     entry = load_profiles().get(self.selected_profile_name, {})
                 if isinstance(entry, dict):
                     self.mixed_voice_state = entry.get("voices", [])
-                    self.selected_lang = entry.get("language")
+                    self.selected_lang = resolve_profile_language(entry)
                 else:
                     self.mixed_voice_state = entry
-                    self.selected_lang = entry[0][0] if entry and entry[0] else None
+                    self.selected_lang = (
+                        language_for_voice_id(entry[0]) if entry and entry[0] else Language.EN_US
+                    )
         if self.save_option == "Choose output folder" and self.selected_output_folder:
             self.save_path_label.setText(self.selected_output_folder)
             self.save_path_row_widget.show()
@@ -1181,6 +1181,7 @@ class abogen(QWidget):
             "Sentence + Comma: Subtitles will be generated for each sentence and comma.\n"
             "Sentence + Highlighting: Subtitles with word-by-word karaoke highlighting.\n"
             "1+ word: Subtitles will be generated for each word(s).\n\n"
+            "Word-count and highlighting modes are only available for English.\n"
             "Supported languages for subtitle generation:\n"
             + "\n".join(
                 f'"{lang}" => {LANGUAGE_DESCRIPTIONS.get(lang, lang)}'
@@ -1759,8 +1760,9 @@ class abogen(QWidget):
 
     def update_subtitle_options_availability(self):
         """
-        Update the enabled state of subtitle options based on the selected language.
-        For non-English languages, only sentence-based and line-based modes are supported.
+        Update the enabled state of subtitle options based on the selected
+        language and input type. Subtitle generation works for every language,
+        but word-count and highlighting modes are only available for English.
         """
         # Check if current file is a subtitle file
         is_subtitle_input = False
@@ -1769,16 +1771,14 @@ class abogen(QWidget):
         ):
             is_subtitle_input = True
 
-        if self.selected_lang not in SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION:
-            self.subtitle_combo.setEnabled(False)
-            self.subtitle_format_combo.setEnabled(False)
-            return
-
         # Only enable subtitle_combo if it's NOT a subtitle input
         self.subtitle_combo.setEnabled(not is_subtitle_input)
         self.subtitle_format_combo.setEnabled(True)
 
-        is_english = self.selected_lang in ["a", "b"]
+        is_english = self.selected_lang in (
+            Language.EN_US,
+            Language.EN_GB,
+        )
 
         # Items to keep enabled for non-English
         allowed_modes = ["Disabled", "Line", "Sentence", "Sentence + Comma"]
@@ -1793,10 +1793,7 @@ class abogen(QWidget):
             if is_english:
                 item.setEnabled(True)
             else:
-                if text in allowed_modes:
-                    item.setEnabled(True)
-                else:
-                    item.setEnabled(False)
+                item.setEnabled(text in allowed_modes)
 
         # If current selection is disabled, switch to a valid one
         current_text = self.subtitle_combo.currentText()
@@ -1815,7 +1812,7 @@ class abogen(QWidget):
 
     def on_voice_changed(self, index):
         voice = self.voice_combo.itemData(index)
-        self.selected_voice, self.selected_lang = voice, voice[0]
+        self.selected_voice, self.selected_lang = voice, language_for_voice_id(voice)
         self.config["selected_voice"] = voice
         save_config(self.config)
         # Enable/disable subtitle options based on language
@@ -1832,10 +1829,12 @@ class abogen(QWidget):
             # set mixed voices and language
             if isinstance(entry, dict):
                 self.mixed_voice_state = entry.get("voices", [])
-                self.selected_lang = entry.get("language")
+                self.selected_lang = resolve_profile_language(entry)
             else:
                 self.mixed_voice_state = entry
-                self.selected_lang = entry[0][0] if entry and entry[0] else None
+                self.selected_lang = (
+                    language_for_voice_id(entry[0]) if entry and entry[0] else Language.EN_US
+                )
             self.selected_voice = None
             self.config["selected_profile_name"] = pname
             self.config.pop("selected_voice", None)
@@ -1845,7 +1844,7 @@ class abogen(QWidget):
         else:
             self.mixed_voice_state = None
             self.selected_profile_name = None
-            self.selected_voice, self.selected_lang = data, data[0]
+            self.selected_voice, self.selected_lang = data, language_for_voice_id(data)
             self.config["selected_voice"] = data
             if "selected_profile_name" in self.config:
                 del self.config["selected_profile_name"]
@@ -1856,8 +1855,9 @@ class abogen(QWidget):
         from abogen.voice_profiles import load_profiles
 
         entry = load_profiles().get(profile_name, {})
-        lang = entry.get("language") if isinstance(entry, dict) else None
-        enable = lang in SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION
+        enable = (
+            resolve_profile_language(entry) in SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION
+        )
         self.subtitle_combo.setEnabled(enable)
         self.subtitle_format_combo.setEnabled(enable)
 
@@ -2239,18 +2239,18 @@ class abogen(QWidget):
         else:
             return self.selected_voice
 
-    def get_selected_lang(self, voice_formula) -> str:
+    def get_selected_lang(self, voice_formula) -> Language:
         if self.selected_profile_name:
             from abogen.voice_profiles import load_profiles
 
             entry = load_profiles().get(self.selected_profile_name, {})
-            selected_lang = entry.get("language")
+            selected_lang = resolve_profile_language(entry)
         else:
-            selected_lang = self.selected_voice[0] if self.selected_voice else None
+            selected_lang = language_for_voice_id(self.selected_voice)
         # fallback: extract from formula if missing
         if not selected_lang:
             m = re.search(r"\b([a-z])", voice_formula)
-            selected_lang = m.group(1) if m else None
+            selected_lang = language_for_code(m.group(1)) if m else Language.EN_US
         return selected_lang
 
     def get_actual_subtitle_mode(self) -> str:
@@ -2426,7 +2426,7 @@ class abogen(QWidget):
             self.update_log((gpu_msg, gpu_ok))
             self.update_log("Loading modules...")
 
-            lang_code = self.selected_lang or "a"
+            lang_code = self.selected_lang or Language.EN_US
             load_thread = LoadPipelineThread(
                 pipeline_loaded_callback, lang_code=lang_code, use_gpu=gpu_ok
             )
@@ -2757,12 +2757,12 @@ class abogen(QWidget):
                 from abogen.voice_profiles import load_profiles
 
                 entry = load_profiles().get(self.selected_profile_name, {})
-                lang_to_cache = entry.get("language")
+                lang_to_cache = resolve_profile_language(entry)
             else:
                 lang_to_cache = self.selected_lang
             if not lang_to_cache and self.mixed_voice_state:
                 lang_to_cache = (
-                    self.mixed_voice_state[0][0][0]
+                    language_for_voice_id(self.mixed_voice_state[0][0])
                     if self.mixed_voice_state and self.mixed_voice_state[0][0]
                     else None
                 )
@@ -2866,7 +2866,7 @@ class abogen(QWidget):
             )
             self.loading_movie.start()
 
-        lang = self.selected_lang or "a"
+        lang = self.selected_lang or Language.EN_US
         load_thread = LoadPipelineThread(
             self._on_pipeline_loaded_for_preview, lang_code=lang, use_gpu=self.gpu_ok
         )
@@ -2898,17 +2898,17 @@ class abogen(QWidget):
                 from abogen.voice_profiles import load_profiles
 
                 entry = load_profiles().get(self.selected_profile_name, {})
-                lang = entry.get("language")
+                lang = resolve_profile_language(entry)
             else:
                 lang = self.selected_lang
             if not lang and self.mixed_voice_state:
                 lang = (
-                    self.mixed_voice_state[0][0][0]
+                    language_for_voice_id(self.mixed_voice_state[0][0])
                     if self.mixed_voice_state and self.mixed_voice_state[0][0]
                     else None
                 )
         else:
-            lang = self.selected_voice[0]
+            lang = language_for_voice_id(self.selected_voice)
             voice = self.selected_voice
 
         # use same gpu/cpu logic as in conversion
@@ -3954,7 +3954,9 @@ Categories=AudioVideo;Audio;Utility;
                     initial_state = entry.get("voices", [])
                 else:
                     initial_state = entry
-                    self.selected_lang = entry[0][0] if entry and entry[0] else None
+                    self.selected_lang = (
+                        language_for_voice_id(entry[0]) if entry and entry[0] else Language.EN_US
+                    )
         dialog = VoiceFormulaDialog(
             self, initial_state=initial_state, selected_profile=selected_profile
         )
diff --git a/abogen/pyqt/voice_formula_gui.py b/abogen/pyqt/voice_formula_gui.py
index 0621fbf..80e1ef9 100644
--- a/abogen/pyqt/voice_formula_gui.py
+++ b/abogen/pyqt/voice_formula_gui.py
@@ -28,7 +28,6 @@ from PyQt6.QtWidgets import (
 from PyQt6.QtCore import Qt, QTimer, QPoint, QRect, QSize
 from PyQt6.QtGui import QPixmap, QIcon, QAction
 from abogen.constants import (
-    SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION,
     LANGUAGE_DESCRIPTIONS,
     COLORS,
 )
@@ -949,7 +948,9 @@ class VoiceFormulaDialog(QDialog):
         lang = state.get("language") if isinstance(state, dict) else None
         # apply language selection
         if lang:
-            i = self.language_combo.findData(lang)
+            from abogen.voice_profiles import resolve_profile_language
+
+            i = self.language_combo.findData(resolve_profile_language(state))
             if i >= 0:
                 self.language_combo.blockSignals(True)
                 self.language_combo.setCurrentIndex(i)
@@ -1571,9 +1572,10 @@ class VoiceFormulaDialog(QDialog):
             parent.selected_profile_name = None
             lang = self.language_combo.currentData()
             parent.selected_lang = lang
-            parent.subtitle_combo.setEnabled(
-                lang in SUPPORTED_LANGUAGES_FOR_SUBTITLE_GENERATION
-            )
+            if hasattr(parent, "update_subtitle_options_availability"):
+                parent.update_subtitle_options_availability()
+            else:
+                parent.subtitle_combo.setEnabled(True)
             # Reset start flag and trigger preview
             self._started = False
             parent.preview_voice()
diff --git a/abogen/spacy_utils.py b/abogen/spacy_utils.py
index dc09f11..1901bfe 100644
--- a/abogen/spacy_utils.py
+++ b/abogen/spacy_utils.py
@@ -57,7 +57,9 @@ def get_spacy_model(language: Language, log_callback=None):
             print(msg)
 
     if not isinstance(language, Language):
-        raise TypeError(f"language must be Language enum, got {type(language).__name__}: {language!r}")
+        raise TypeError(
+            f"language must be Language enum, got {type(language).__name__}: {language!r}"
+        )
 
     if language in _nlp_cache:
         return _nlp_cache[language]
diff --git a/abogen/voice_profiles.py b/abogen/voice_profiles.py
index 1841348..9df4c7d 100644
--- a/abogen/voice_profiles.py
+++ b/abogen/voice_profiles.py
@@ -2,6 +2,7 @@ import json
 import os
 from typing import Any, Dict, Iterable, List, Tuple
 
+from abogen.domain.enums import Language
 from abogen.tts_plugin.utils import get_voices, is_plugin_registered
 from abogen.utils import get_user_config_path
 
@@ -176,13 +177,35 @@ def save_profile(name: str, *, language: str, voices: Iterable) -> None:
         raise ValueError("At least one voice with a weight above zero is required")
 
     if not language:
-        language = "a"
+        language = Language.EN_US
 
     profiles = load_profiles()
     profiles[name] = {"provider": "kokoro", "language": language, "voices": normalized}
     save_profiles(profiles)
 
 
+def resolve_profile_language(entry: Any) -> Language:
+    """Resolve a profile's stored language to a Language enum.
+
+    New profiles store ISO codes (Language enum values); legacy profiles may
+    store kokoro letter codes ("a", "b", ...). Unparseable values fall back
+    to EN_US.
+    """
+
+    raw = entry.get("language") if isinstance(entry, dict) else None
+    if isinstance(raw, Language):
+        return raw
+    text = str(raw or "").strip()
+    if not text:
+        return Language.EN_US
+    try:
+        return Language.from_str(text)
+    except ValueError:
+        from plugins.kokoro.engine import language_for_code
+
+        return language_for_code(text)
+
+
 def remove_profile(name: str) -> None:
     delete_profile(name)
 
diff --git a/plugins/kokoro/engine.py b/plugins/kokoro/engine.py
index 2440691..e1d0b6e 100644
--- a/plugins/kokoro/engine.py
+++ b/plugins/kokoro/engine.py
@@ -73,17 +73,27 @@ def engine_language(lang: Language) -> str:
     return _KOKORO_LANG_MAP.get(lang, "a")
 
 
-def language_for_voice_id(voice_id: str) -> Language:
+def language_for_code(code: str | None) -> Language:
+    """Map a kokoro engine language code (single letter) to a Language enum.
+
+    Used to resolve legacy data such as old profile files that stored
+    kokoro letter codes. This is kokoro-specific knowledge that stays
+    inside the engine. Unparseable values fall back to EN_US.
+    """
+    letter = str(code or "").strip()[:1].lower()
+    if letter in _CODE_TO_LANGUAGE:
+        return _CODE_TO_LANGUAGE[letter]
+    return Language.EN_US
+
+
+def language_for_voice_id(voice_id: str | None) -> Language:
     """Determine which Language a voice belongs to from its voice ID.
 
     Kokoro voice IDs encode language as a prefix (e.g. "af_heart" → "a" → EN_US).
     This is kokoro-specific knowledge that stays inside the engine.
     Callers pass a voice ID string; the engine returns a Language enum.
     """
-    prefix = str(voice_id or "").strip()[:1].lower()
-    if prefix in _CODE_TO_LANGUAGE:
-        return _CODE_TO_LANGUAGE[prefix]
-    return Language.EN_US
+    return language_for_code(voice_id)
 
 
 class KokoroSession:
diff --git a/tests/test_enums.py b/tests/test_enums.py
index c5cc422..a31ba66 100644
--- a/tests/test_enums.py
+++ b/tests/test_enums.py
@@ -119,7 +119,7 @@ class TestLanguage:
     def test_supports_subtitle_tokens(self):
         assert Language.EN_US.supports_subtitle_tokens is True
         assert Language.EN_GB.supports_subtitle_tokens is True
-        assert Language.ZH.supports_subtitle_tokens is False
+        assert Language.ZH.supports_subtitle_tokens is True
 
     def test_from_str_case_insensitive(self):
         assert Language.from_str("EN-US") == Language.EN_US
@@ -129,3 +129,8 @@ class TestLanguage:
     def test_from_str_invalid(self):
         with pytest.raises(ValueError, match="Invalid Language"):
             Language.from_str("en")
+
+    def test_kokoro_letter_codes_not_accepted_by_domain(self):
+        # Letter codes are kokoro-engine internals, not domain API.
+        with pytest.raises(ValueError):
+            Language.from_str("a")
diff --git a/tests/test_kokoro_plugin.py b/tests/test_kokoro_plugin.py
index a73f800..6ce1f2b 100644
--- a/tests/test_kokoro_plugin.py
+++ b/tests/test_kokoro_plugin.py
@@ -196,3 +196,42 @@ class TestKokoroVoiceLister:
             assert isinstance(voice.tags, tuple)
             assert len(voice.tags) > 0
         engine.dispose()
+
+
+# ──────────────────────────────────────────────────────────────
+# Language mapping helpers
+# ──────────────────────────────────────────────────────────────
+
+class TestKokoroLanguageMapping:
+    """Language resolution helpers: the letter codes live in the engine only."""
+
+    def test_language_for_code(self) -> None:
+        from abogen.domain.enums import Language
+        from plugins.kokoro.engine import language_for_code
+
+        assert language_for_code("a") == Language.EN_US
+        assert language_for_code("b") == Language.EN_GB
+        assert language_for_code("e") == Language.ES
+        assert language_for_code("f") == Language.FR
+        assert language_for_code("h") == Language.HI
+        assert language_for_code("i") == Language.IT
+        assert language_for_code("j") == Language.JA
+        assert language_for_code("p") == Language.PT_BR
+        assert language_for_code("z") == Language.ZH
+
+    def test_language_for_code_fallbacks(self) -> None:
+        from abogen.domain.enums import Language
+        from plugins.kokoro.engine import language_for_code
+
+        assert language_for_code("x") == Language.EN_US
+        assert language_for_code("") == Language.EN_US
+
+    def test_language_for_voice_id(self) -> None:
+        from abogen.domain.enums import Language
+        from plugins.kokoro.engine import language_for_voice_id
+
+        assert language_for_voice_id("af_heart") == Language.EN_US
+        assert language_for_voice_id("bf_emma") == Language.EN_GB
+        assert language_for_voice_id("ef_dora") == Language.ES
+        assert language_for_voice_id("zf_xiaobei") == Language.ZH
+        assert language_for_voice_id("") == Language.EN_US
diff --git a/tests/test_voice_profiles.py b/tests/test_voice_profiles.py
new file mode 100644
index 0000000..0edcb97
--- /dev/null
+++ b/tests/test_voice_profiles.py
@@ -0,0 +1,28 @@
+"""Tests for voice profile language resolution."""
+
+from __future__ import annotations
+
+from abogen.domain.enums import Language
+from abogen.voice_profiles import resolve_profile_language
+
+
+class TestResolveProfileLanguage:
+
+    def test_iso_code(self) -> None:
+        assert resolve_profile_language({"language": "en-US"}) == Language.EN_US
+        assert resolve_profile_language({"language": "es"}) == Language.ES
+
+    def test_enum_value(self) -> None:
+        assert resolve_profile_language({"language": Language.ZH}) == Language.ZH
+
+    def test_legacy_kokoro_letter(self) -> None:
+        assert resolve_profile_language({"language": "a"}) == Language.EN_US
+        assert resolve_profile_language({"language": "e"}) == Language.ES
+        assert resolve_profile_language({"language": "z"}) == Language.ZH
+
+    def test_missing_or_unparseable_falls_back(self) -> None:
+        assert resolve_profile_language({}) == Language.EN_US
+        assert resolve_profile_language({"language": ""}) == Language.EN_US
+        assert resolve_profile_language({"language": "xx"}) == Language.EN_US
+        assert resolve_profile_language(None) == Language.EN_US
+        assert resolve_profile_language([]) == Language.EN_US
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