plugin is not working anymore

It sounds to me like whatever has changed on your system is breaking Ajax requests.

it was working perfectly until this day.

What might have changed since it last worked? Did your version of Loco Translate change? Did you update any other plugins? What about your theme? Has your hosting provider made any changes to any server settings or any software?

When opening or triyng to create a file with your plugin, this error message …

You should never see that raw JSON on the screen, because it’s not actually an error; it’s a success message. Did you “Check console output for debugging information”?

Do you get any errors on the diagnostics page? Go to Loco Translate > Settings > Debug (and make sure WordPress debug mode is on).

Also try this FAQ for how to get more information on Ajax errors.

Error: {“data”:{“authed”:true,”valid”:[],”creds”:[],”method”:”direct”,”success”:”Connected to remote file system”}}

Your message has “fancy” quote characters. not regular " quotes. Is this what you actually get back from the server, or is this just how they appear on this forum?

I solved the problem this morning!
It was a conflict with the latest update of my server firewall.
I deactivated it and the plugins works perfectly now!
I now just need to find a new way to secure my site.
Thanks for your reply

Thanks for marking as resolved, but it will help others (and me) if you explain a bit more. What was the Firewall software? What was the update?

Some firewalls are known to break WordPress Ajax, but you shouldn’t have to disable them completely. Ask your hosting provider whether there are some rules you can change, then please post what you find works.

It’s the OVH firewall (an optionnal free firewall on the french hosting company OVH).
Their support told me that several users experienced problems since yesterday, and that they are working on it. No additionnal news from them yet.