That looks very weird and to be honest, I don't think it is caused by our plugin.
However, my recommendation for you is to try this:
- First, create a full backup of your site's files and database
- Log via FTP or inside your hosting panel
- go to your site's directory
- go to wp-content
- change the name of the "plugins" folder to "plugins2" (what should this do is disable all the plugins on your site)
- see if you can access the site now
If you can access the site now, try to rename the /plugins directory back to the default one and the plugins should be disabled in the backend.
Now, enable each of them until you find the one that is creating the issue.
If you are sure this was caused by our plugin, instead of renaming the whole /plugins directory, you could simply go inside the /plugins directory and rename the folder name of our plugin from "sitepress-multilingual-cms" to "sitepress-multilingual-cms2"