Also raise original error message in util.get_lang_class

Otherwise, the true error that happens within a Language subclass is swallowed, because if it's imported lazily like that, it'll always be an ImportError

spacy/errors.py

@@ -177,7 +177,7 @@ class Errors(object):
             "you forget to call the `set_extension` method?")
     E047 = ("Can't assign a value to unregistered extension attribute "
             "'{name}'. Did you forget to call the `set_extension` method?")
-    E048 = ("Can't import language {lang} from spacy.lang.")
+    E048 = ("Can't import language {lang} from spacy.lang: {err}")
     E049 = ("Can't find spaCy data directory: '{path}'. Check your "
             "installation and permissions, or use spacy.util.set_data_path "
             "to customise the location if necessary.")

spacy/util.py

@@ -53,8 +53,8 @@ def get_lang_class(lang):
     if lang not in LANGUAGES:
         try:
             module = importlib.import_module(".lang.%s" % lang, "spacy")
-        except ImportError:
-            raise ImportError(Errors.E048.format(lang=lang))
+        except ImportError as err:
+            raise ImportError(Errors.E048.format(lang=lang, err=err))
         LANGUAGES[lang] = getattr(module, module.__all__[0])
     return LANGUAGES[lang]