gh-142714: Keep the PEG grammar out of the translation catalogs

The grammar in reference/grammar.rst was extracted into the .pot files
verbatim, including the parts that PEGLexer hides from the rendered page.
There is nothing to translate there, so mark PEG literal blocks as not
translatable.

Author: Aurora-NICExq

Doc/tools/extensions/lexers/__init__.py

@@ -1,12 +1,27 @@
+from docutils import nodes
+from sphinx.transforms import SphinxTransform
+
 from .asdl_lexer import ASDLLexer
 from .peg_lexer import PEGLexer
 
 
+class UntranslatablePEGBlocks(SphinxTransform):
+    # The grammar has nothing to translate, so keep it out of the
+    # message catalogs. Must run before the i18n Locale transform (20).
+    default_priority = 10
+
+    def apply(self):
+        for node in self.document.findall(nodes.literal_block):
+            if node.get("language") == "peg":
+                node["translatable"] = False
+
+
 def setup(app):
     # Used for highlighting Parser/Python.asdl in library/ast.rst
     app.add_lexer("asdl", ASDLLexer)
     # Used for highlighting Grammar/python.gram in reference/grammar.rst
     app.add_lexer("peg", PEGLexer)
+    app.add_transform(UntranslatablePEGBlocks)
 
     return {
         "version": "1.0",