So the right way would be to set up one main category for each language and then a subcategory for each site ?

There is no right or wrong way, it is up to you. I personally would suggest you to just use one category for each theme and translate it's name using JText, the same as other options in drop downs. To show articles from certain category and language you just need to add this 2 fields to the search type.

Regarding automatic translation I am not aware of any existing solution that would work with Seblod.

For search/list, just add some field with translation states to the form, then you can filter by it.

Hi Klas, 

thanks for suggestion, but I don't undersand well what do you mean with "I personally would suggest you to just use one category for each theme and translate it's name using JText, the same as other options in drop downs..."

Also, What do you mean with "theme" ?

Many Thanks for help

Theme = topic. No need for language specific categories, create categories for each topic..or content type or similar (just in main language). When article is shown and JText is activated you can use select simple, which allows translation of it's options, to show translated category name (but you will need to manually enterr all categories and their ids). Hopefully soon translation will also be possible with select dynamic,which can be used with simple query to replace jform category field without manual entries.

Hi Klas, I'm not sure I understood. As far as I understand you mean to use the second solution mentioned by Seblod:

2 - Single item for all languages.

If so, this was not my question. I'd prefer to use the Joomla way (to keep the compatibility with all the other components installed, Google SEO etc.) and the question is How to organize languages in case I'll need to use the Seblod Multisite feature that, as we know (at least as was at the begin), suggest to creat a main category for each sub-site.

I add, Do you have any suggestions for the question A:

A - A way where I wrote the articles in one language and prefill the other articles for the other languages. Thinking to use Google Translate for it (for example), Is there a way to do it automatically ? (not copy and past).

No, I'm just telling you Joomla way of having category for each language is unnecessary complication with Seblod. Joomla needs it as category list or blog uses only category for filtering while in Seblod you just need to add language as additional filter (and you can translate category names as described).

For A answered you already:

Regarding automatic translation I am not aware of any existing solution that would work with Seblod.

Hi Klas, thanks.

1 - "Joomla needs it as category list or blog uses only category for filtering while in Seblod you just need to add language as additional filter (and you can translate category names as described)":
Logically if the Language Category have no content, but it is just an "Organizing" Category. Am I right ?

2 - About your Select Dynamic feature "Bug Enanched", Can you give me an example of its practical use ?

3 - Just thinking if that can cause any problem with Joomla and/or other components installed. I asked also on Joomla here

4 - Anyway thinking on Site (Joomla+Seblod) that could be transformed in a Seblod Muti Site,
- Is a main Category (for each site on multi site) still a need for Seblod ?
- At the begin, on the main site, Is a main Category a must, or we could create it in future avoiding an unnecessary complication at the begin ?

5 - Sorry I mistake, I mean point B - I'll have some users that should translate the articles for some languages (if there is no the "A" solution), or check and and correct the prefilled translated articles and confirm the check-in (and/or publish them). Do you have any suggestion on create a Lists & Search Type like this one where the user can have an entire list of the unchecked / untranslated articles and work on them ?

I think you need to re-read my previous answers, I don't know how to explain my ideas in a different way.