Comment 5 for bug 1705393

The problème remains if I switch to the official repos :

deb http://fr.archive.ubuntu.com/ubuntu/ xenial main restricted universal
deb http://security.ubuntu.com/ubuntu xenial-security main restricted universal
deb http://fr.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universal

I check the php7.0-mbstring package here :

https://packages.ubuntu.com/fr/xenial/php7.0-mbstring

And it says the package depends on php7.0-common (= 7.0.4-7ubuntu2)

which is similary to my apt install error message :

php7.0-mbstring : Depends: php7.0-common (= 7.0.4-7ubuntu2) but 7.0.18-0ubuntu0.16.04.1 is to be installed