I would concur that a gap in your CV in first year will not look weak. Work will be a plus, but I wont go as far as Mars to say that shelf stacking would be seen as productive (I did this for financial reasons - but it didn't even make my CV!).
When we look to hire undergrads, we generally look at:
- Extracurriculars. Ideally try to lead one substantial society (Varsity, Union, CUSU, Boat Club, JCR, etc...) or several smaller ones. The aim is to show (i) leadership and (ii) transformation/change
- Grades. Do not let yourself slip into 2:2 territory.
- Work. I had no internships whatsoever and got interviews at MBB based on above. However, particularly for a linguist, being able to demonstrate some business sense is important, whether through internships or volunteering or clubs/societies. Remember the experience is key - we prefer high impact roles even at small firms (e.g. running your own start up) than irrelevant big brand experience (e.g. trading at GS). A second year internship is fine.
- Interest. Unfortunately lots of amazing people from Cambridge apply each year. Make your CV stand out
I would focus on these things in your first year, but not worry if your Summer looks empty.