Hi Cyrille,
Found that the font file is giving 404 not found error. http://www.steffgruber.com/de/wp-content/uploads/useanyfont/190418083834steff_roman.woff/
Can you please make sure this font file 190418083834steff_roman.woff is available in this folder wp-content/uploads/useanyfont/ ? If this exists, then there is high chance woff font loading has been blocked by your server. In that case, please try adding this in your htaccess file. The above link will not give 404 when the blocked is removed.
<FilesMatch "\.(ttf|otf|eot|woff|woff2|css)$">
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin "*"
</IfModule>
</FilesMatch>
If this doesn’t work, please ask your host provider to enable font (woff and woff format) for loading.
.
