On 2018-03-21, Dr Rainer Woitok <rainer.woitok(a)gmail.com> wrote:
Warning: Cannot convert string
"-*-helvetica-bold-r-*-*-*-120-*-*-*-*-iso8859-*" to type FontStruct
Alternatively, you could install the font (and whatever comes with
it).
I'm also on Xubuntu 16.04.
Try installing xfonts-75dpi and xfonts-100dpi