CWEB, Plain TeX: how to switch from cmr8 to another font that supports foreign language characters?

You have to define a suitable font for \eightrm, but also setup some uppercase conversions; here I define only those necessary for the examples.

There was also an unfortunate typo in utfplainmac.tex, with \c{A} instead of the correct \c{C}. Fix it in the file.

\input cwebmac
\input utfplainmac
\input plain-t1

\font\eightrm=ecrm0800

\uccode"A7="87 % ç is <C3><A7>, Ç is <C3><87>
\uccode"A3="83 % ã is <C3><A3>, Ã is <C3><83>

\N{1}{1} Introdução. Lorem ipsum dolor...

\bye

There is an alternative using pdfcsplain:

\input cwebmac
\input utf8lat1
\input lmfonts

\N{1}{1} Introdução. Lorem ipsum dolor...

\end