"It is Wednesday today."
Translation:Det är onsdag i dag.
In Swedish, it needs to be "today, it is Wednesday = i dag är det onsdag" which is just a reordered version of "it is Wednesday today = det är onsdag i dag".
"today is Wednesday = i dag är onsdag" is not accepted because there is no subject in the Swedish sentence. In English, the word 'today' can be a time expression, an adverb meaning "during the 24 hours between yesterday and tomorrow"; and it can also be a noun meaning "the day that includes the current moment". Because of this, you can use it as a subject of a sentence "today is beautiful" or as an adverb "today we met again". In Swedish you can only use it as an adverb, it isn't a noun.
Same applies to 'i morgon', 'i kväll', 'i natt', and the like