Before purchasing I would like to know if JMS can solve this scenario:

Lets say I have a joomla installation with joomfish, virtuemart and sh404 in spanish language under www.spanish.org domain.

I have translated the site to portuguese using joomfish, and I now want to have the translated www.spanish.org site, under the domain www.portuguese.org, with its own SEF urls, but showing all the translated products and content of the www.spanish.org site.
Joomfish translations, orders, products and users must be managed only from the www.spanish.org site (the master site).
Each site will have its own management for sh404 urls, as I dont think it's possible to manage the diferent domain sef urls on the master site.

In the future I will also have www.french.org, www.german.org etc etc

Can JMS handle this scenario?

NO it is not really possible like that.

The problem in your description is that you are using a website with JoomFish to perform the translation in different language.
You could have several domain that point to the same websites and share the same content.

If you share your website between different domain, this will also share the SH404 or perhaps the "alias" the you provide in the articles and perhaps also in your product (if you can decide of the alias) could be probably the same between the websites.
So share the same website might not work with SH404

If you decide to have specific website for each domain, the problem is to share the content between the website. I don't know with extension you are using for the product.
If this is VirtueMart, it is possible to share VM between the websites.
In this case, the problem will be the translation with JoomFish.
JoomFish can not be shared between the websites.

So if you decide to share VirtueMart, you will have to perform the translation in each specific lanquage into each slave site (probably with a JoomFish).

So the only solution that you should check with a prototype would be to create different slave sites corresponding to each domain.
Share the VirtueMart extension between the slave site.
Use a specific JoomFixh in each slave site to perform the translation in its specific language.
So you will not have 1 joomfish but as many joomfish as you have language to translate (1 per domain or slave site).

Ok, that would be a good solution.
To be clear:
There will be a joomla website and domain for each language, each site will have it's own joomfish translation and SH044.
Virtuemart products AND pictures will be added through one of the installations and shared between all the sites. (That would be perfect).
Could I also share the main menu and content from the master site with the other sub sites?
Thanks for your help.

The main menu and other content are not shared.

If you want moreless share the main menu, you have the "Multisties Menu Item" that allow creating a bridge between websites menu item (not the menu itself).
Concerning the other content, the word "content" is too generic.
You can share a limited number of extension "content" and if you want to share the article content you need the "Article Sharing for JMS".
You also have the "Multisites Contact Sharing" to share the contact content.

www.jms2win.com/download?page=shop.produ...pl&product_id=34
www.jms2win.com/components/com_virtuemar...size=90&fileout=
www.jms2win.com/download?page=shop.produ...pl&product_id=43

Ok, but Virtuemart is 100% shareable? (orders, products, product pictures, templates, etc, etc)?

YES you can share ALL the VM tables.
See the list of extension that can be shared
www.jms2win.com/component/content/article/135