texinfo.tex ver. 2016-05-28.15 renames
commondummies to definedummies.
So we need to replace it which we use.
\DeclareUnicodeCharacter{2116}{\textnumero}
-% Add all Cyrillic character names to \commondummies.
+% Add all Cyrillic character names to \definedummies.
\gdef\cyrdummies{%
\definedummyword\textnumero
\definedummyword\cyrudoubleacute
}
-\toks0 = \expandafter{\commondummies\cyrdummies}
-\xdef\commondummies{\the\toks0}
+\toks0 = \expandafter{\definedummies\cyrdummies}
+\xdef\definedummies{\the\toks0}
% Add all Cyrillic character names to \indexnofonts.