Applying for internship in the US as a European Student
As has been said, your last sentence hits the mark - a direct comparison is impossible.  I would argue that it isn't necessary, either.

I am a US native.  I am currently working an internship in the United States at a child company of a larger pharmaceutical business.  I know that my company had a "minimum" GPA for the application, but this was never mentioned in the interviewing process.  To me this implies that companies use GPA to see if a candidate meets a satisfactory minimum - it's a way to weed out applicants they know they don't want or need.  I think if you explain that your GPA is good by European standards, if indeed it is, then your application will be strong.

A few of my fellow interns are from Germany.  I don't know them well but I mention this to show that success is possible and that some companies in the United States, at least, have a good grasp of how grading scales work in Europe.  I think it worth mentioning that Europe seems to have a relatively smaller amount of grade inflation as compared to here.  That's an important point - grades are somewhat inflated here, and a 3.5 GPA probably indicates a level of performance that is different than you imagine.  Given this, I would say your chances of getting a job are good, especially if you adopt the normal tactics of applying to many positions and being prepared to take a few rejections.