今日はとても暇でした。英語でなんて言うの？

1. Slack = decrease or reduce in intensity, quantity, or speed.
   "The flow of blood slacked off."
   "business in the outdoor market this morning was slacker than usual."
2. This means the volume of customers coming into the shop is low.
   "All Quiet On The Western Front is a novel by Erich Maria Remarque, a German veteran of World War I. The sentence means that there is little activity between the opposing forces.
3. This comment is about the probably bad condition of the weather affecting the number of customers coming into the shop.

"It's slow today." This explains that there are not many customers so business is slow and there is now much to do.

"It's very quiet today." this means that there are not many customers and that business is slow. There is not much work to do.

*We usually don't get lot of customers when it is raining or cold.
This means that if the weather is bad a lot of people do not visit the store.
For example:
Coworker: There are not a lot of people today.
You:We usually don't get lot of customers when it is raining or cold.

(a place) is dead - this means that the place is quiet; without any activity

empty - this means that a place is without people

very little traffic - in this case, it is referring to "foot traffic," or the movement of people into and out of the store

Its very quiet at the shop today.- quiet meaning that there are not that many customers in the shop.
The weather must be putting people off shopping. - meaning = the weather is bad so no one wants to come shopping.
Its a slow day at the store today. slow, meaning that there aren't that many customers- the day seems to go very slowly because its not so busy.

You can also say...
Its so quiet today.
Wow today has dragged so much (the day seems long)
Time is dragging on today
This day seems to go on forever
We've hardly had any customers today.
*Where is everyone (customers) its so dead today.

When you say 'its dead today'- in this context it means there's no one around, or its very quiet.

Hope this helps! ^ ^

Because of the bad weather, there aren't many customers today.
- This explains the cause of not having many customers. You can also say, "Because of the rain/cold. . ."

Thanks to the weather, there's barely anyone here today.
- This also states the cause of the lack of customers. You can also just say, "There's barely anyone here today."

Today is very slow.
- This refers to the business being slow, which is because of the lack of customers.

If you want to express that you don't have the same flow of customers everyday and some days are busier than others, you can use the following sentences:-

1. Some days are slower than others.
   (Slower here refers to the flow of customers.)

2. We do not have a lot of customers everyday.

3. It's not a busy everyday.

Quiet means when there is no noise or bustle. With other words, there is silence in the store. The first sentence doesn't explain the reason but still can be used.