Turning that question round to an English perspective, it all depends on the command and understandability of the speaker which would set my preference.
So, if you are generally understood, and you will know it, keep on going. A favourite joke of mine after speaking French to a stranger who detects my accent is 'how on earthe did you guesse? In French of course and with mock surprise. Most of us have an accent of some sort or another and not necessarily a bar to comprehension.
I speak good French but writing is harder. I want to make myself understood so I have no hesitation using a good translation system like DeepL to write longer emails. It rarely makes mistakes and I can spot the occasional one and adjust it. I have no doubt that the recipient prefers to receive the mail in French.
Speaking is another question. If I speak in French I prefer that they reply in French. With a doctor, because of terminology, I might ask if they speak English and we then decide who speaks the other language better. Knee doctor speaks fluent English. Dermatologist speaks English but badly, so we agree to do it in French with a bit of Franglais and not too fast and to explain technical terms.
Yesterday a young assistant in Castorama wanted to practice her English. If she got stuck I would help in French. She prepared a full devis for a new bathroom (in French of course).
In conclusion itâs a delicate balance.
There is a great expression in FrenchâŠ.parler comme une vache espagnol
Do Spaniards confuse English people with cows then? 
I have a group of motorcycling friends who are all French who live all over the place. I see them several times a year. When I am with them French is spoken so they know the level of my French and they accept me mistakes and all. I keep in touch with them individually and as a group via WhatsApp. We have been arranging a weekend away in the Auvergne in early September and that has generated a lot of posts. When I post on WhatsApp I use a translator, itâs quick and easy and I want my short messages to be correct. I always mentally work out the French in my head before using the translator. That then becomes a learning exercise. Sometimes I use the translator back to front, I type in my French and it gives me the English translation. I then flip it to get the âcorrectedâ French. None of my friends would object to me checking my posts.
I am replying to myself because although connected to my post it off topic.
Last Monday I went down to Perigueux to have lunch in a particular restaurant. I checked on Google and it said it would be open so I set off on the 160km motorbike ride. I arrived at midday to find the place closed. I checked online and found a FB post explaining that their opening hours had changed and that they were now closed on Mondays. I messaged the chef. I asked if he was at home. He replied. He was. I asked if it would be OK to call in to see him at home later. He asked if I had eaten. I replied, no. I was invited to lunch.
The chef is the person from the group who I met first and most of the other members are his longtime friends. I havenât seen him as much as usual this year because for one reason or another only one or the other of us could make it to several of the events we go to. A couple of weeks ago he had had to pull out of another one because of staff problems at work. He went on to say that he had not only had to work an extra day a week so was now working 6/7 but his two week summer holiday had had to be cancelled. I told him that I would call in at the restaurant soon and say hello. Unbeknown to me the restaurant had decided to temporarily close on Mondays to ease the workload. Nobody told Google.
In the end it all worked out fine. I spent the whole afternoon with Phillippe and his wife (and new grey kitten) and was also treated to a fabulous lunch.
Isnât that rather outdated/inappropriate now as I understood it refers to French Basque people insulting Spanish servants whose French was not great. Nothing to do with cows.
Might you not get away with it if you used it to refer to yourself in a self-deprecating way?
I usually just say âDĂ©solĂ© pour mon français atroce je suis anglaisâ. 
Hugely outdated. Totally politically incorrect. But as per Mike I have used it self deprecating my own accent.
I have come to an agreement with my consultant in Lyon, alternate languages.
My consultant in Macon speaks excellent English which helps Jim understand too.
I help out with his consultant who only speaks French.
Whoâs Mike?
Great story
Lately, seems many in Spain may prefer cows.
Only sâils parlent français comme une vache espagnole, apparently.
I am just back from the vampire cave (laboratoireâŠ) where a young and not unattractive nurse sucked some blood out of me. As she was quite talkative, I asked her what her take was on the likes of me babbling on in rubbish French. She likes the English accent but went on to say that my accent is so terrible that she wants to give me a big hug and teach me French.
She suggests I continue as is!
Jeez, there are times that I wish I was thirty five years younger⊠
Me too⊠I recently discovered (because she revealed it in a video) that the gorgeous Nelly who I learn French from on YouTube is just 28⊠
Pseudonym of some guy called Chris Mann.
A senior moment overcame me!!!
Mike Chan 
Yes, and you would have to be sure of your ground.
For example , you would not want to get the symptoms of constipation and diarrhoea confused.
I do the sameâŠbeing Scottish. 
