There are some howtos on the internet decribing how to convert a vCard based address book to LDIF, so you can import it into Claws mail personal address book. All of these use an online converter, which seemed a little bit dangerous to me, since I don’t know what the server does with my address book data aside from converting it.
But there is a much simpler way.
When you open your address book you can just go to “Book -> New vCard” and specify the path to your vCard-File in the File-field. This will create a new entry under “vCard” in your address book. All you have to do now is to copy all entries to your personal address book by dragging and dropping them. Afterwards you can delete created vCard by selecting it and clicking “Book -> Delete book”.
That’s all! Pretty easy, huh?