Juries are most certainly not a universal part of the legal system. They are mostly found in the Anglosphere. Most European countries, for example, have a civil law system that typically does not feature a jury of peers.

Are prosecutors allowed to imply in closing arguments that asserting one's fifth amendment right should be considered evidence that the person is guilty? I would hope that judges would instruct juries not to consider assertion of this right as evidence one way or another, and would not allow a prosecutor to say so either.

It seems that this is the case, based on Griffin v California: https://caselaw.findlaw.com/us-supreme-court/380/609.html

> Comment to the jury by a prosecutor in a state criminal trial upon a defendant's failure to testify as to matters which he can reasonably be expected to deny or explain because of facts within his knowledge or by the court that the defendant's silence under those circumstances evidences guilt violates the Self-Incrimination Clause of the Fifth Amendment of the Federal Constitution

isn't the jury system an american thing?