which export format did you use?
Open it with a text editor and see if the quotations are in there. If they are we can likely do something from the Zotero side, otherwise you'll need to find a way to get that data out of Citavi first.
I don't think we'll write a direct export from Citavi's database (which I believe is MS Access based?) but there may be other ways.
Find out from Citavi if the quotation info is in any export they provide.

Following up on this one: Citavi support told me that I could re-name the .ctv-file (that contains all the data of a project) into .mdb and then simply open it with MS-Access.
That worked indeed, but now I'm stuck: I do see all the data, but everything in different tables, some containing all the book titles, others all the authors, etc. And one chart also contains all the quotations. But how can I make Zotero import that and link it accordingly?
Any help is appreciated.

Thank you for the quick reply again, although, of course, that definitively brings my import ambitions to a dead halt. And I doubt that Citavi (being a for-profit-company) is interested in telling me how to get away from their programme.
If anyone reads this and knows how to proceed with the code (i.e. using the .mdb-file to import into Zotero), please revive this thread! I presume that quite a few people might be interested in that.

You are right about both Citavi support (they are friendly and helpful) and about the slippery slope of nevertheless ending up being a "hostage" of their product.
From what I have gathered, Citavi is basically two programmes rolled into one: A bibliography manager quite like Zotero, and a knowledge management software (that's the part where the quotations are). They linked these two quite nicely together in their software, but the downside is that their bibliographies use .bib or .ris formats, while the knowledge management is MS-Access-based. Being quite unfamiliar with both of these formats, I simply do not know how to proceed to bring the latter into a form that can be read by Zotero (or any other bibliography manager, for that matter), e.g. converting it into notes attached to the item. Citavi support told me that there simply is no field in the .bib or .ris-files to export this kind of data.
Or maybe, by using Access, I could somehow create a whole new sqlite-database from the .mdb-file and then somehow merge that with the Zotero-database that already contains some items, but as mentioned, with my limited knowledge of Access, I am simply stuck here.

I'll look into this when I have some time. I'd be interested in adding support for Citavi -> Zotero migration. Probably will take me a while though

As another acquaintance has come across the same issue here (after I recommended Zotero), I'd like to resurrect this thread and enquire if there is anything on the horizon concerning easy Citavi-to-Zotero-migration. Anything, anyone?

Apologies, I digged into this further and found that the Zotero team already developed a dedicated Citavi importer and a solution is posted here: https://www.zotero.org/support/kb/import-from-citavi

Many thanks!

Could you open the .ctv5 file with a text editor and post the first ~10 lines here, please? You'll need to put <code> before them and </code> after them so they show up properly.

Yes, that doesn't look right at all. Zotero is looking for something like this:
https://gist.github.com/zuphilip/02d6478ace4636e4e090e348443c551e

But I'm just seeing that this may require Citavi 5 upwards, so it's possible this won't work with Citavi 4 -- @zuphilip do you happen to know?

That worked fine but the backups files *.ctv5bak do not behave like zip files but like normal files

What happens when you open a Terminal in the directory where that file is (right-click on the folder > “Services” > “New Terminal at Folder”) and run:
unzip [File].ctv5bak

@dstillman @noksagt
Thanks!!

Like dstillman I didn't see that option so I did what he said.
The result was:
MacBook-Air:~ sina$ cd filename.ctv5bak
-bash: cd: filename.ctv5bak: Not a directory
MacBook-Air:~ sina$ unzip filename.ctv5bak
Archive: filename.ctv5bak
inflating: firsthalfoffilename.ctv5
MacBook-Air:~ sina$

But no new files showed up at the original location.

@bwiernik
:) Thanks!
It indeed got me one step further - but unfortunately only that:
So I repeated the same thing with the Folder now, then unzipped the file, and indeed a new file *.ctv5 was created at the same location. When I imported this file in Zotero, it didn't complain about the format, created a library with the accurate name but then reported a problem, asking me to check whether the file was correct and try again.

Who can help me get to the next level? (Thanks so much in advance!)

and in addition to that the exact error message you're getting (untranslated) as well as well as an error report ID: https://www.zotero.org/support/reporting_problems right after this occurs.

error message:
Fehler _ Ein Fehler ist aufgetreten beim Importieren der ausgewählten Datei. Bitte überprüfen Sie, ob die Datei korrekt ist und versuchen Sie es erneut.

@dstillman could you take a look at the error, please
@zuphilip can you tell if the Citavi XML looks right?