I want to use a variable for a font size so I can set it based on language (as some translated texts have widely different sizes)

This fails:

%===========================

\newdimen\relationsFontSize
\relationsFontSize=8pt
\starttext
\switchtobodyfont[\relationsFontSize]
Hello, world!
\stoptext

How can I use a variable to steer \switchtobodyfont size?