diff --git a/alfred/domain/shared/value_objects.py b/alfred/domain/shared/value_objects.py
index 30c74ee..b468a2e 100644
--- a/alfred/domain/shared/value_objects.py
+++ b/alfred/domain/shared/value_objects.py
@@ -1,5 +1,7 @@
 """Shared value objects used across multiple domains."""
 
+from __future__ import annotations
+
 import re
 from dataclasses import dataclass
 from pathlib import Path
@@ -142,19 +144,49 @@ class Language:
             raise ValidationError(
                 f"Language.iso must be a 3-letter ISO 639-2/B code, got {self.iso!r}"
             )
-        # Normalize iso to lowercase
-        object.__setattr__(self, "iso", self.iso.lower())
-        # Normalize aliases to a tuple of lowercase strings (dedup, preserve order)
+        if self.iso != self.iso.lower():
+            raise ValidationError(
+                f"Language.iso must be lowercase, got {self.iso!r} — "
+                f"use Language.from_raw() to construct from arbitrary input"
+            )
+        for alias in self.aliases:
+            if not isinstance(alias, str) or alias != alias.lower().strip() or not alias:
+                raise ValidationError(
+                    f"Language.aliases must be lowercase non-empty strings, "
+                    f"got {alias!r} — use Language.from_raw() to normalize"
+                )
+
+    @classmethod
+    def from_raw(
+        cls,
+        iso: str,
+        english_name: str,
+        native_name: str,
+        aliases: tuple[str, ...] | list[str] = (),
+    ) -> Language:
+        """
+        Construct a Language from arbitrary (possibly un-normalized) input.
+
+        Use this factory when loading from external sources (YAML, user input,
+        third-party APIs) — it lowercases the iso code and normalizes/dedups
+        the alias tuple. The direct constructor is strict and rejects
+        un-normalized input.
+        """
         seen: set[str] = set()
         normalized: list[str] = []
-        for alias in self.aliases:
+        for alias in aliases:
             if not isinstance(alias, str):
                 continue
             a = alias.lower().strip()
             if a and a not in seen:
                 seen.add(a)
                 normalized.append(a)
-        object.__setattr__(self, "aliases", tuple(normalized))
+        return cls(
+            iso=iso.lower(),
+            english_name=english_name,
+            native_name=native_name,
+            aliases=tuple(normalized),
+        )
 
     def matches(self, raw: str) -> bool:
         """
diff --git a/alfred/infrastructure/knowledge/language_registry.py b/alfred/infrastructure/knowledge/language_registry.py
index e3734b3..7ae3f45 100644
--- a/alfred/infrastructure/knowledge/language_registry.py
+++ b/alfred/infrastructure/knowledge/language_registry.py
@@ -87,7 +87,7 @@ class LanguageRegistry:
         merged = _merge_language_entries(builtin, learned)
 
         for iso, entry in merged.items():
-            language = Language(
+            language = Language.from_raw(
                 iso=iso,
                 english_name=entry.get("english_name", iso),
                 native_name=entry.get("native_name", iso),