\input plain

\font\roman=pbyk8r at 16pt

% Acutes
\def\'#1{\def\arg{#1}\def\a{a}\def\e{e}\def\i{i}\def\ii{\i}\def\o{o}\def\u{u}%
\def\A{A}\def\E{E}\def\I{I}\def\II{\I}\def\O{O}\def\U{U}%
\ifx\arg\a\char225 \fi%
\ifx\arg\e\char233 \fi%
\ifx\arg\i\char237 \fi%
\ifx\arg\ii\char237 \fi%
\ifx\arg\o\char243 \fi%
\ifx\arg\u\char250 \fi%
\ifx\arg\A\char193 \fi%
\ifx\arg\E\char201 \fi%
\ifx\arg\I\char205 \fi%
\ifx\arg\II\char205 \fi%
\ifx\arg\O\char211 \fi%
\ifx\arg\U\char218 \fi}

% Dieresis
\def\"#1{\def\arg{#1}\def\a{a}\def\e{e}\def\i{i}\def\ii{\i}\def\o{o}\def\u{u}%
\def\A{A}\def\E{E}\def\I{I}\def\II{\I}\def\O{O}\def\U{U}%
\ifx\arg\a\char228 \fi%
\ifx\arg\e\char235 \fi%
\ifx\arg\i\char239 \fi%
\ifx\arg\ii\char239 \fi%
\ifx\arg\o\char246 \fi%
\ifx\arg\u\char252 \fi%
\ifx\arg\A\char196 \fi%
\ifx\arg\E\char203 \fi%
\ifx\arg\I\char204 \fi%
\ifx\arg\II\char207 \fi%
\ifx\arg\O\char214 \fi%
\ifx\arg\U\char220 \fi}

% For ~n
\def\~#1{\def\arg{#1}\def\n{n}\def\N{N}%
\ifx\arg\n\char241 \fi%
\ifx\arg\N\char209 \fi}


\roman

\setbox0\hbox{VÄ}
\showthe\wd0
\setbox1\hbox{V\"A}
\showthe\wd1
\end