Hi Matt,
This is a difficult time but it isn't the end of the world. Your wife clearly knows that something isn't right, and that something is desperately wrong. She just doesn't know. The refraining from speaking is part of the 'flight, fright and fight' responses that we all have built into us. She is responding to the situation by not speaking at all, which in itself should be telling you loads. Perhaps her language processing is becoming compromised, this is not simply what she receives but what she expresses which has subsequently caused her to feel as if she is failing. This is huge for people living with dementia, suddenly they find people are looking at them strangely and they don't know why - was it something I said? Eventually their conversation reduces to social chit-chat, everyday rhythmic chat such as 'hi how are you? I'm good, and you?' No true content or substance.
Ask your wife what she would like to do, reassure her that you are there to support her and not take over for her. Do get on to your GP, and district nurse to organise a home visit so they can assess your wife for care hours, which does help you to maintain your relationship and not suddenly feel overwhelmed by a carer role.
What I can say is don't talk to her like she is a child, and don't talk to her as if she has hearing loss. Continue to show her the respect and dignity that you have always given to your wife. Put signs up on doors, to help her way-find to the kitchen and bathroom. There are fabulous dementia friendly clocks that will help her and your to orientate to time, day, month.
What is meaningful to your wife? That is the important thing. If she has always enjoyed knitting, bring her to a yarn shop and let her enjoy looking about. Keeping her condition a secret won't benefit her at all, so if you live in a town or village, let shopkeepers / owners know - especially those shops that your wife would be inclined to frequent. As her dementia progresses you will discover how incredibly helpful their knowing is.
If she still doesn't want to do things that she once found meaningful, ask her to help you.
We can't help but want to help people, especially those we care about. She's still the same person, only different.
I would definitely keep the radio and the television to timed 'activity' pursuits - if there is a specific tv show or radio show then watch or listen to that and then turn it off. Otherwise the background noise does become a stressor and can lead to agitation. The urge sometimes to let our loved one sit before a tv screen when we 'get on with stuff' is very strong but don't get in to the habit. Have her help you, she clearly still wants to feel useful and needed.
Helping to hang clothes up, to put clothes into a washing machine, to stack a dishwasher or rinse the dishes, set the table, help to dress the bed, cleaning, sweeping, gardening .... there is a litany of things that your wife is very capable of doing still. Perhaps working on her life story together in the evening might also be a lovely way for your both to reminiscence after a long day.
Hope some of this helps you,
Linda