we tried to use this extension.
We tried a lot, but it was too difficult.
The migration tool from Joomfish is fully bugged.
All the article ID were wrong.
It works if you have less than 100 items... very strange.
And Josetta does not seem to sort the article items.
We asked some help to the Josetta Team, but no significants results.
So just one advise, don't use this extensions if you have more than 100 articles.
Sorry you had so much trouble, but I think I can provide some information for you here:
It is NOT technically possible to keep the same article ids when moving from Joomfish to Joomla native multilingual system.
Very simply, the two systems don't work the same way: Joomfish had only on article id for all languages, while Joomla basically creates several articles, one per language, each with its own id.
Therefore, ids cannot be the same.
Josetta tries to do its best with this, and that's why we scan every menu, every article and automatically replace the ids to match the new ones, so that links in menus and articles are not broken after importing.
Note that in the process, we also adjust the urls, as Joomla has changed also its internal links: from view=frontpage to view=featured, removal of "section", moved to category,etc
Likewise, categories and sections are turned into nested Joomla categories, and ids adjusted where needed (ids cannot be the same, just like for articles or any other type of content)
As for "not working with more than 100 items", I just have no idea what you mean by that.
Josetta is routinely used by fairly large sites, with several thousands articles in multiple languages.
It seemed we had a terrible time communicating that message to you during the many exchanges we had on the forum, I hope it's clearer here and now.