diff --git a/sdk/basyx/aas/model/base.py b/sdk/basyx/aas/model/base.py
index f6b55fa8..3edaac6e 100644
--- a/sdk/basyx/aas/model/base.py
+++ b/sdk/basyx/aas/model/base.py
@@ -301,11 +301,36 @@ def __init__(self, dict_: Dict[str, str]):
 
     @classmethod
     def _check_language_tag_constraints(cls, ltag: str):
-        split = ltag.split("-", 1)
-        lang_code = split[0]
-        if len(lang_code) != 2 or not lang_code.isalpha() or not lang_code.islower():
-            raise ValueError(f"The language code of the language tag must consist of exactly two lower-case letters! "
-                             f"Given language tag and language code: '{ltag}', '{lang_code}'")
+        alphanum = "[a-zA-Z0-9]"
+        singleton = "[0-9A-WY-Za-wy-z]"
+        extension = f"{singleton}(-({alphanum}){{2,8}})+"
+        extlang = "[a-zA-Z]{3}(-[a-zA-Z]{3}){0,2}"
+        irregular = (
+            "(en-GB-oed|i-ami|i-bnn|i-default|i-enochian|i-hak|"
+            "i-klingon|i-lux|i-mingo|i-navajo|i-pwn|i-tao|i-tay|"
+            "i-tsu|sgn-BE-FR|sgn-BE-NL|sgn-CH-DE)"
+        )
+        regular = (
+            "(art-lojban|cel-gaulish|no-bok|no-nyn|zh-guoyu|zh-hakka|"
+            "zh-min|zh-min-nan|zh-xiang)"
+        )
+        grandfathered = f"({irregular}|{regular})"
+        language = f"([a-zA-Z]{{2,3}}(-{extlang})?|[a-zA-Z]{{4}}|[a-zA-Z]{{5,8}})"
+        script = "[a-zA-Z]{4}"
+        region = "([a-zA-Z]{2}|[0-9]{3})"
+        variant = f"(({alphanum}){{5,8}}|[0-9]({alphanum}){{3}})"
+        privateuse = f"[xX](-({alphanum}){{1,8}})+"
+        langtag = (
+            f"{language}(-{script})?(-{region})?(-{variant})*(-{extension})*(-"
+            f"{privateuse})?"
+        )
+        language_tag = f"({langtag}|{privateuse}|{grandfathered})"
+
+        pattern = f"^{language_tag}$"
+
+        if re.match(pattern, ltag) is None:
+            raise ValueError(f"The language tag must follow the format defined in BCP 47. "
+                             f"Given language tag: {ltag}")
 
     def __getitem__(self, item: str) -> str:
         return self._dict[item]
diff --git a/sdk/test/model/test_base.py b/sdk/test/model/test_base.py
index 98c6cfb8..b40174b5 100644
--- a/sdk/test/model/test_base.py
+++ b/sdk/test/model/test_base.py
@@ -1230,20 +1230,28 @@ def hook(itm: int, _list: List[int]) -> None:
 
 class LangStringSetTest(unittest.TestCase):
     def test_language_tag_constraints(self) -> None:
+        with self.assertRaises(ValueError):
+            model.LangStringSet({"": "bar"})
+
         with self.assertRaises(ValueError) as cm:
-            model.LangStringSet({"foo": "bar"})
-        self.assertEqual("The language code of the language tag must consist of exactly two lower-case letters! "
-                         "Given language tag and language code: 'foo', 'foo'", str(cm.exception))
+            model.LangStringSet({"x": "bar"})
+        self.assertEqual(f"The language tag must follow the format defined in BCP 47. "
+                         f"Given language tag: x", cm.exception.args[0])
 
-        lss = model.LangStringSet({"fo-OO": "bar"})
         with self.assertRaises(ValueError) as cm:
-            lss["foo"] = "bar"
-        self.assertEqual("The language code of the language tag must consist of exactly two lower-case letters! "
-                         "Given language tag and language code: 'foo', 'foo'", str(cm.exception))
-        self.assertNotIn("foo", lss)
-        self.assertNotIn("fo", lss)
-        lss["fo"] = "bar"
-        self.assertIn("fo", lss)
+            model.LangStringSet({"foo-oo1": "bar"})
+        self.assertEqual(f"The language tag must follow the format defined in BCP 47. "
+                         f"Given language tag: foo-oo1", cm.exception.args[0])
+
+        lss = model.LangStringSet({"fo-OO": "bar"})
+        self.assertIn("fo-OO", lss)
+        with self.assertRaises(ValueError):
+            lss["foo-oo1"] = "bar"
+        self.assertNotIn("foo-oo1", lss)
+
+        self.assertNotIn("foo-ASDF-OO", lss)
+        lss["foo-ASDF-OO"] = "bar"
+        self.assertIn("foo-ASDF-OO", lss)
 
     def test_empty(self) -> None:
         lss = model.LangStringSet({"fo": "bar", "fo-OO": "baz"})