In the Netherlands, specialist talk about dialects (regionalisms) but also about sociolect.
And what is colloquial style? Is that how people speak, or is it also ‘informal writing’ ?

The definition I used was country variant, but it can be extended and used as you need to. I haven’t thought that deeply on what should be included on that category.
My understanding of “colloquial style” is defined as the “default” spoken language, usually considered informal, when compared with typical written texts.