What is the situation like in Paris in late December 2019?

From a safety point of view, the main reported risk is that road accidents involving bikes and motorbikes show a 40% progression. Apart from this, nothing more or less than usual.

Regarding transportation, automatic subway lines (1 and 14) are up but are expected to be overcrowded. Transportation from and to airports is more difficult.

About food, Rungis, the main "farmer's" market also called the "belly of Paris", expects some difficulties but is prepared to the situation. Their main concern is more in the lack of sales than in the lack of incoming products.

Nevertheless, usually when strikes arise in december, they stop during Christmas time. This is the so-called "Trève de Noël". This may or may not be the case this year. Unions are still debating on this point.

Transport woes aside, Paris is functioning pretty much normally. People take much longer to get to work, but they get there. A few shops are having irregular hours. Streets are packed (with additional vehicles, not people overspilling form the sidewalks). There is absolutely no shortage in services or supplies.

I won't reiterate the other answers, but the main challenges for tourists are:

• Aside from the 1 and 14 metro lines, transport is affected. You will take longer and/or it will be more expensive to move around. I'd say a bike will or walking will be the best option.
• A few flights and most of the trains in and out of the city are affected.
• Public museums are affected (e.g. the louvre says that they may open later and/or close some exhibition rooms depending on the circumstances)
• Many opera performances were cancelled
• The Eiffel tower has already been closed twice, there is a risk it'll happen again

On the plus side: The center of Paris is fairly compact and most areas are quite walkable - it is much less spread out than Tokyo, for example.

I've been to Paris from 07. Dec to 10. Dec while there was strike (see question) and virtually no Metro was running. Arriving by car in the 9th Arrondisment was kind of a nightmare, but once the car was parked (make sure to reserve and pay for a spot in a car park beforehand!) I did not have the impression of pure chaos in Paris.

Of course it depends on where you are. Given your accomodation is somewhere in the city with reasonable walking distances, it is nice to discover Paris by foot. Public transport was kind of out of question, because the few busses where packed with people.

So if the situation at the end of the month will anything like in the beginning, I guess you will be fine. Restaurants and hotels were working as usual, so I guess they will continue to do so.