'\v{C}' character not rendered in fonts which don't have 'Č' with T1 encoding

The font misses several precomposed accented glyphs. At the expense of the possibility to hyphenate the words containing Č, you can do

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[sf,scaled=0.9]{quattrocento}

\providecommand*\UndeclareTextComposite[3]{%
  \expandafter\let\csname\expandafter\string\csname
  #2\endcsname\string#1-#3\endcsname\relax}

\UndeclareTextComposite{\v}{T1}{C}

\begin{document}

\textsf{\v{C}}
\textbf{\textsf{\v{C}}}

\end{document}

enter image description here

See https://tex.stackexchange.com/a/58115/4427 for \UndeclareTextCompositeCommand. Do similarly for other missing accented characters you need.

It's immaterial whether you use \v{C} or directly Č.

Note. The maintainer of the LaTeX font package remarked that the glyphs are missing because they're not even in the OpenType font the TeX version is derived from.