If you are using form factor then all items will still be shown on your Wix Editor, however the ones that are set for another version should be set as hidden on load.
As shown here in this tutorial for only showing on mobile.
https://support.wix.com/en/article/corvid-tutorial-displaying-elements-in-mobile-only
API reference.
https://www.wix.com/corvid/reference/wix-window.html#formFactor
I have used the mobile option on my own website for showing a different logo in my header than to the desktop version and to change the icon for the mobile menu instead of using the existing hamburger icon and it all works perfectly.
On your desktop editor and your mobile editor, the other version that you have hidden, let us say mobile for now, however yours will be the other language, will still be shown although they will be tinted on the screen as they are set up as hidden on load in both desktop and mobile editors.
To view this code fully working, you need to test your website on a fully published version on a desktop or mobile and not just use the preview mode only.
If you are wanting to edit each Wix Form separately, then I suggest that you move each Wix Form so that they are up on the screen together without overlapping each other. Then when you are finished with them both, you can simply place both Wix Forms back into their original positions.
However, you might prefer to want to make up your own user input forms through code with your own datasets and not just use Wix Forms and it’s Submission Tables.
https://support.wix.com/en/wix-multilingual/wix-multilingual-basics
https://www.wix.com/corvid/reference/wix-window.multilingual.html
Also, make sure that you set it up in your mobile editor too.
https://support.wix.com/en/article/multilingual-menu-on-your-mobile-friendly-site
If it still doesn’t work then you can try simply swapping the hide and show calls for the unwanted form and change it to collapse and expand instead so that it is collapsed and isn’t simply hidden from view.
https://www.wix.com/corvid/reference/$w.HiddenCollapsedMixin.html