Some packages which are “supposed” to be installed during the yunohost installed were not, because of this specific piece of config. c.f. this issue : What do with setups with Install-Recommends set to 'false' ? · Issue #1320 · YunoHost/issues · GitHub
Running the following command should avoid any future trouble related to this :
apt install php-gd php-curl php-gettext php-mcrypt