Schwedische Grammatik

sorry for replying in English, my written German is not good enough (yet).

Anyway, for me who speaks perfect Swedish the main difference between "denna vackra dag" and "den här vackra dagen" is that:

"Denna vackra dag" says nothing about any other days, it states that today is a beautiful day but does not mention any other days.

I disagree regarding formeller-schriftsprach versus umgangssprachlich, the form "denna vackra dagen" sounds very old for me and the only time I would prefer it would be when writing poetry, if you use "den här vackra dagen" it is more likely to be appropriate for the context.