hello everyone
To install MonoGame 3.5 on your Xubuntu / Ubuntu I recommend to use MonoDevelop 6. To do execute following commands
mkdir ~/Apps
mkdir ~/Apps/Monodevelop
mkdir ~/.local/share/applications
sudo apt-get update
sudo apt-get -y upgrade
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo “deb Index of /repo/debian wheezy main” | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
sudo apt update && sudo apt upgrade -y
sudo apt install -y autoconf automake cmake fsharp git gnome-sharp2 gtk-sharp2 libssh2-1-dev mono-complete referenceassemblies-pcl zlib1g-dev
cd ~/Apps/Monodevelop
git clone GitHub - mono/monodevelop: MonoDevelop is a cross platform .NET IDE --branch monodevelop-6.1.2.44 --depth 1 6.1.2.44
cd 6.1.2.44
./configure --profile=stable --enable-release
make
make run