There was a response to this on another "Nous sommes [day]" sentence. The explanation given was that if you were exclaiming that the day was Tuesday, you would say "Nous sommes mardi." But, if someone asked "Qu'est-ce que la journée?"*, you would reply "C'est mardi."
*I apologise that that is probably a terrible, badly worded way of asking what day it is.
That's what you get when you do a word-for-word translation. Unfortunately, doing that can and sometimes will give you a wrong result as happens in this case.
In French, there are two ways of stating the current day. You can say either of the following:
Aujourd'hui c'est [day]
Today it is [day] (word-for-word; almost correct)
Today is [day] (correct)
Nous sommes [day]
We are [day] (word-for-word; incorrect)
Today is [day] (correct)
The situation you describe is an unfortunate side-effect of living in a multilingual city/town. The languages used there tend to infiltrate into each other resulting in a 'corruption' of the languages.
This is quite evident where I live (Kumasi, Ghana); we have words from English creeping into, and often replacing the original words of the local language, Twi. We also have some Twi expressions being taken word-for-word into English (e.g.: It is quite common to find a person saying "I am coming" instead of "I will be right back").
It may be a bit odd finding that the expressions used in your local variant of the language is incorrect but that is the way it is. The correct usage of the language will always be constant.
"I am coming" is perfectly normal, standard English.
Languages influence each other all the time, and it's neither good nor bad. "Correct" usage actually constantly changes, so you needn't worry.
Both English and French are the way they are because of the influence of other languages, and are all the richer for it. What's important is that you try to speak the way natives do when learning a language.
Alex, Ghana . Official language is English and is compulsory in schools .There are around 80 languages in Ghana . You to say English words are creeping in to 'twi ' ? 'Twi' is one of two dialects of 'Akan' sponsored by government 80% live below $2 a day and most vendors ( streets are full of them) cannot speak much English and communicate mainly in 'twi' but all official business is in English . Even the taxi drivers and 'VIP coach' ( called VIP as a trade name , comfortable coaches made in China) attenders speak English fluently . Thus you will have ' Twi' creeping in to conversations in English !
You are right in your observation, Omar.
With more people becoming fluent in both languages, it is becoming more common to find Twi creeping into English conversations and vice versa.
One must be quite careful when having a conversation lest a word suddenly 'jumps' across the language barrier! :-)
I've heard the phrase "we are in [day]" in English among people with virtually no foreign language experience (in N.E. United States). It has the same effect, but the literal meaning is something more existential, like "the time has moved on and now we are all in the current day". I've mostly heard it in response to a mistaken day, not a direct question, like:
"I thought it was Wednesday" "No, we're in Thursday".
Think in French, speak in French. Think in English, speak in English. But not think in French, speak in English. I.e., there is no "we are Tuesday" in English. The French phrase must be expressed in natural English, not a literal word-for-word "translation". Another way to say this is that French idioms work in French but are not imported directly (literally) to English.
It's the same analogy as the English word tomorrow.
Tomorrow is a composite of two words, to + morrow where to is the regular preposition and morrow means 'the following day'.
I reckon that we don't normally use hui in everyday speech for the same reason that we don't normally use 'morrow' in English.
It doesn't translate literally from the latin as 'day' - there is ownership implied, loosely it is something like 'the day we have/are having', so aujourd'hui becomes something like 'on the day we have/on the day we are having', but the 'hui' is an archaic fragment which does not stand alone in usage, as Alex.Essilfie said much in the way that 'morrow' is not often bandied about in English.