Go to Google Font site. Choose the desired font in Google Fonts.
Click the Add to Collection button next to your favorite font.
Now download your fonts collection. (You can even download the entire google fonts family!)

Unzip the font file. Go to your fonts directory and create a folder for the downloaded font:

cd /usr/share/fonts/truetype/
sudo mkdir name_of_the_font

Now move the content of the zip file to the newly created folder:

sudo mv ~/Escritorio/Font_file.ttf ./

Restart LibreOffice. Now you can see the font in the list!