Thanks for your inquiry in our Agile Multiple Seller/vendor module - a best PrestaShop based online market place solution.
1) Is the module multilanguages?
we need to support some European languages on frontside and on vendorside.
Yes, PrestaShop support multiple language, you can install any language Package, and use the Translation function of PrestaShop to translate into any language you want to use.
2) Themes compatibility: Can we use the themes available for prestashop, or should we use special themes if we have your module installed?
You can use any theme the is compatible with PrestaShop.
3) Are the images compressed?
I mean, we would like to let sellers to upload big images (i.e 8Mega) and that those images show quickly on website pages because they have been compressed and are now 100/200K). Is it possible?
PrestaShop generate different size of thumbnail images uses for different scenarios.
User can download original image size as attachment.
Also,in your DEMO, we tried (many times) to upload an image (8Mega, 18Mpixel), but without success: is there a problem to upload big images, with a lot of pixels? is there a workaround?
There is limit upload size by PrestaShop and also your server web server limit.
But you can change/increase the limit size to what you want.
4) Do you plan to build a mobile compatibility version in the future?
The module does not support mobile site theme - This is not currently compatible with mobile themes.
This does not mean mobile devices cannot use your PrestaShop site. Nowdays mobile devices and smart phones are able to access/use almost all normal websites, so it may not be necessary for you to create a special site for mobile devices.
If not, do you think it is a big work to modify this our-self?
You can implement by yourself.
But it will depend on your knowledge on PrestaShop and mobile theme.