Refactor locale validation and update style consistency across schemas, tests, and migrations

- Replaced `SUPPORTED_LOCALES` with `supported_locales` for naming consistency.
- Applied formatting improvements to multiline statements for better readability.
- Cleaned up redundant comments and streamlined test assertions.

backend/app/alembic/versions/c8e9f3a2d1b4_add_user_locale_preference_column.py

@@ -23,10 +23,7 @@ def upgrade() -> None:
     # VARCHAR(10) supports BCP 47 format (e.g., "en", "it", "en-US", "it-IT")
     # Nullable: NULL means "not set yet", will use Accept-Language header fallback
     # Indexed: For analytics queries and filtering by locale
-    op.add_column(
-        "users",
-        sa.Column("locale", sa.String(length=10), nullable=True)
-    )
+    op.add_column("users", sa.Column("locale", sa.String(length=10), nullable=True))
 
     # Create index on locale column for performance
     op.create_index(

backend/app/api/dependencies/locale.py

@@ -117,8 +117,9 @@ async def get_locale(
     if current_user and current_user.locale:
         # Validate that saved locale is still supported
         # (in case SUPPORTED_LOCALES changed after user set preference)
-        if current_user.locale in SUPPORTED_LOCALES:
-            return current_user.locale
+        locale_value = str(current_user.locale)
+        if locale_value in SUPPORTED_LOCALES:
+            return locale_value
 
     # Priority 2: Accept-Language header
     accept_language = request.headers.get("accept-language", "")

backend/app/schemas/users.py

@@ -40,9 +40,9 @@ class UserUpdate(BaseModel):
     locale: str | None = Field(
         None,
         max_length=10,
-        pattern=r'^[a-z]{2}(-[A-Z]{2})?$',
+        pattern=r"^[a-z]{2}(-[A-Z]{2})?$",
         description="User's preferred locale (BCP 47 format: en, it, en-US, it-IT)",
-        examples=["en", "it", "en-US", "it-IT"]
+        examples=["en", "it", "en-US", "it-IT"],
     )
     is_active: bool | None = (
         None  # Changed default from True to None to avoid unintended updates
@@ -70,12 +70,12 @@ class UserUpdate(BaseModel):
             return v
         # Only support English and Italian for template showcase
         # Note: Locales stored in lowercase for case-insensitive matching
-        SUPPORTED_LOCALES = {"en", "it", "en-us", "en-gb", "it-it"}
+        supported_locales = {"en", "it", "en-us", "en-gb", "it-it"}
         # Normalize to lowercase for comparison and storage
         v_lower = v.lower()
-        if v_lower not in SUPPORTED_LOCALES:
+        if v_lower not in supported_locales:
             raise ValueError(
-                f"Unsupported locale '{v}'. Supported locales: {sorted(SUPPORTED_LOCALES)}"
+                f"Unsupported locale '{v}'. Supported locales: {sorted(supported_locales)}"
             )
         # Return normalized lowercase version for consistency
         return v_lower