Stranded wire is only any good if your devices and connectors are rated for the use of stranded wire without ferrules or other terminals. Most designed for the central European market aren't, so using stranded building wire introduces additional labour costs. Coarse stranded wire as is common in Scandinavia is only used for sizes of 10 mm2 and larger here. In Germany cables up to 16 mm2 have solid conductors! I hate to imagine working with them, solid 6 mm2 is annoying enough in tight spaces!
AFAIK Britain and Norway are the only countries in Europe that still allow reduced-size earth conductors smaller than 16 mm2 and the only two that commonly use bare earth conductors in building wiring (Ireland started requiring full-sized isolated earth conductors a year ago I think but I'm not sure if that's already affected actual wiring practices).
Then there's the divide between flat and round cables for building wiring - the UK, Norway and a couple of Eastern European countries predominantly use flat, the others round cables. Not much harmonisation there to see.
