They should be placed in the following folders
For personal use
TTF files in ~/.local/share/fonts/truetype
(old way was ~/.fonts/truetype
)
OTF files in ~/.local/share/fonts/type1
(old way was ~/.fonts/type1
)
For system wide use
TTF files in /usr/local/share/fonts/truetype
OTF files in /usr/local/share/fonts/type1
Then sudo fc-cache
and you should see the fonts.
An alternative way is to place fonts generally in ~/.local/share/fonts/
(old way was ~/.fonts/
).
Can you see the new fonts in Libre Office or similar office programs?
sudo fc-cache
...?