Rename xx to mul in docs

spacy/tests/test_language.py

@@ -556,6 +556,7 @@ def test_spacy_blank():
         ("is", "isl"),
         ("pt-BR", "pt"),
         ("xx", "mul"),
+        ("mul", "mul"),
         ("zh-Hans", "zh"),
         ("zh-Hant", None),
         ("zxx", None),
@@ -579,6 +580,7 @@ def test_language_matching(lang, target):
         ("mo", "ro"),
         ("is", "isl"),
         ("xx", "mul"),
+        ("mul", "mul"),
         ("no", "nb"),
         ("pt-BR", "pt"),
         ("zh-Hans", "zh"),

website/docs/usage/models.md

@@ -83,9 +83,9 @@ import Languages from 'widgets/languages.js'
 
 spaCy also supports pipelines trained on more than one language. This is
 especially useful for named entity recognition. The language ID used for
-multi-language or language-neutral pipelines is `xx`. The language class, a
+multi-language or language-neutral pipelines is `mul`. The language class, a
 generic subclass containing only the base language data, can be found in
-[`lang/xx`](%%GITHUB_SPACY/spacy/lang/xx).
+[`lang/mul`](%%GITHUB_SPACY/spacy/lang/mul).
 
 To train a pipeline using the neutral multi-language class, you can set
 `lang = "mul"` in your [training config](/usage/training#config). You can also