I was having problems with websites requiring the Helvetica family-font in their css: all special french and german characters were replaced by unrelated russian characters.That put me on the track of Helvetica. I have launched font-manager, to check about Helvetica. And when I enter custom text, the font is simply wrong.Example text: tre, spcial, dj, ae, bcher, ffentlich,  whreVisual result:How could I fix the Helvetica font so as it displays properly ?Edit:locate Helvetica returns:/usr/lib/libreoffice/share/psprint/fontmetric/Helvetica-Bold.afm/usr/lib/libreoffice/share/psprint/fontmetric/Helvetica-BoldOblique.afm/usr/lib/libreoffice/share/psprint/fontmetric/Helvetica-Oblique.afm/usr/lib/libreoffice/share/psprint/fontmetric/Helvetica.afm/usr/share/fonts/downloaded_unknown_copyright_use/Helvetica.ttf/usr/share/fonts/type1/mathematica/Helvetica-Bold.afm/usr/share/fonts/type1/mathematica/Helvetica-BoldOblique.afm/usr/share/fonts/type1/mathematica/Helvetica-Oblique.afm/usr/share/fonts/type1/mathematica/Helvetica.afm/usr/share/matplotlib/mpl-data/fonts/pdfcorefonts/Helvetica-Bold.afm/usr/share/matplotlib/mpl-data/fonts/pdfcorefonts/Helvetica-BoldOblique.afm/usr/share/matplotlib/mpl-data/fonts/pdfcorefonts/Helvetica-Oblique.afm/usr/share/matplotlib/mpl-data/fonts/pdfcorefonts/Helvetica.afm/usr/share/perl5/Font/Metrics/Helvetica.pm/usr/share/perl5/Font/Metrics/HelveticaBold.pm/usr/share/perl5/Font/Metrics/HelveticaBoldOblique.pm/usr/share/perl5/Font/Metrics/HelveticaOblique.pm
Russian characters instead of French or German, with Helvetica font
fonts
The file Helvetica.ttf had unknown origins. I have deleted this file and everything is back in order now. It is also possible to install a free variant of Helvetica that can be found here:  Helvetica Neue, it works ok. 