Oh wow congrats on the offers! There are several layers of discussion towards your question.

(1) Taking one more internship as a whole:

From my perspective, it is always good to have more different yet related internship experience on your CV, esp if you are still in year 2 and it seems to me and possibly HR that you are a competitive young talent as you have quite some different intern exp already. Taking a 6-month gap is not demanding, but it would be ideal if you can find another 6-month intern right after your Unicredit internships, as it is better to graduate during the summer time in order to fit with grad recruitment schedule.

(2) Taking a gap sem:

Do you have any financial pressure that you shouldn't delay your graduation date?

(3) Unicredit:

Purely talking about Unicredit, it may not a must-worthwhile institution that you should sacrifice one sem, unless the department is highly related to your desired career path. It also seems to me not many direct graduate opportunities for their interns are provided after internship. So, it depends on whether the dept really suits your career goal.

I guess taking through these questions in your head and you should be able to find an answer for yourself too! Lastly, you may wish to check out some ex-interns' profiles for your reference:

Source: LinkedIn