Fix lang check and error handling in Language.from_config

spacy/errors.py

@@ -552,7 +552,10 @@ class Errors:
             "to register a simple stateless function component that just takes "
             "a Doc and returns it.")
     E958 = ("Language code defined in config ({bad_lang_code}) does not match "
-            "language code of current Language subclass {lang} ({lang_code})")
+            "language code of current Language subclass {lang} ({lang_code}). "
+            "If you want to create an nlp object from a config, make sure to "
+            "use the matching subclass with the language-specific settings and "
+            "data.")
     E959 = ("Can't insert component {dir} index {idx}. Existing components: {opts}")
     E960 = ("No config data found for component '{name}'. This is likely a bug "
             "in spaCy.")

spacy/language.py

@@ -1487,7 +1487,7 @@ class Language:
         if "nlp" not in config:
             raise ValueError(Errors.E985.format(config=config))
         config_lang = config["nlp"]["lang"]
-        if cls.lang is not None and config_lang is not None and config_lang != cls.lang:
+        if config_lang is not None and config_lang != cls.lang:
             raise ValueError(
                 Errors.E958.format(
                     bad_lang_code=config["nlp"]["lang"],

spacy/tests/test_language.py

@@ -5,6 +5,7 @@ from spacy.tokens import Doc, Span
 from spacy.vocab import Vocab
 from spacy.training import Example
 from spacy.lang.en import English
+from spacy.lang.de import German
 from spacy.util import registry
 
 from .util import add_vecs_to_vocab, assert_docs_equal
@@ -266,3 +267,13 @@ def test_language_custom_tokenizer():
     assert [t.text for t in doc] == ["_hello", "_world"]
     doc = list(nlp.pipe(["hello world"]))[0]
     assert [t.text for t in doc] == ["_hello", "_world"]
+
+
+def test_language_from_config_invalid_lang():
+    """Test that calling Language.from_config raises an error and lang defined
+    in config needs to match language-specific subclasses."""
+    config = {"nlp": {"lang": "en"}}
+    with pytest.raises(ValueError):
+        Language.from_config(config)
+    with pytest.raises(ValueError):
+        German.from_config(config)