Fix setlang redirect normalization for locale variants

mandelstudio/i18n_utils.py

@@ -21,11 +21,17 @@ def normalize_set_language_next(value: str | None) -> str:
     if not path.startswith("/"):
         path = f"/{path}"
 
-    language_codes = [code for code, _ in settings.LANGUAGES]
-    if language_codes:
-        pattern = (
-            rf"^/(?:{'|'.join(re.escape(code) for code in language_codes)})(?=/|$)"
-        )
-        path = re.sub(pattern, "", path, count=1) or "/"
+    configured_codes = {
+        str(code).lower().replace("_", "-") for code, _ in settings.LANGUAGES
+    }
+    first_segment, _, remainder = path.lstrip("/").partition("/")
+    normalized_segment = first_segment.lower().replace("_", "-")
+    looks_like_language_code = bool(
+        re.fullmatch(r"[a-z]{2}(?:-[a-z]{2})?", normalized_segment)
+    )
+    should_strip = normalized_segment in configured_codes or looks_like_language_code
+
+    if should_strip:
+        path = f"/{remainder}" if remainder else "/"
 
     return urlunsplit(("", "", path, parsed.query, ""))