Add additional locales to PHP containers

[scq]

Currently the PHP containers only contain en_AU and en_US locales, which makes it hard to test anything to do with locale formatting (e.g. dates) as you have to patch the Dockerfiles and rebuild.

It would be useful to have some non English locales included out of the box. German is a common one we test with, along with Arabic or Hebrew for RTL. Maybe worth adding another couple of European languages too.