Comment 2 for bug 1578821

The explanation is probably that hunspell-gl, provided by libreoffice-dictionaries, is present in 16.04, and hunspell-gl-es conflicts with the former. Suppose we should drop hunspell-gl for now.

A workaround until this has been fixed is to install the Galician translations from a terminal window:

sudo apt install language-pack-gl language-pack-gnome-gl

Then you can run the check-language-support command, and manually install the listed packages, except for hunspell-gl.