We are currently maintaining country folders like
www.example.net/de/
www.example.net/fr/
Now we are thinking about Swiss with 3 languages (it, de, fr). I think it's bad to change all the current directories. Is it okay to only add the region if necessary? For example:
www.example.net/de/ = German speaking, not Swiss
www.example.net/fr/
www.example.net/it/
www.example.net/de-CH/ = German speaking, Swiss only
www.example.net/it-CH/
www.example.net/fr-CH/
So: Is it for SEO okay to mix the subfolder structure between /lang/
& /lang-country/
?