Think of a guilty/not guilty plea as the defense declaring their stance rather than literally saying "I did this" or "I did not do this". After all there are circumstances in which a person absolutely did the thing they're accused of but are not actually guilty (self defense) or extenuating circumstances need to be considered (insanity plea).

Perjury requires that a person lied under oath in a specific, provable way. That's why defense attorneys will sometimes have their client not take the stand or assert their fifth amendment rights in response to certain questions. Making the prosecution prove that the defendant did a thing is fine. Saying "I didn't do thing X at all" and then having evidence being presented that you did is no bueno.

TL;DR: A not guilty plea basically says "prove it". Perjury is lying about specifics and it can later be proved beyond a reasonable doubt that you lied about those details.

Simple answer is no. You have a constitutional right to say not guilty because it’s innocent until proven guilty.

A plea is not a testimony, and the defendant is not under oath at that point, so a not guilty plea is not seen as perjury. However, the defendant rejects any deals by pleading not guilty, so it might result in a more severe sentence.

(edit) There is also an option of "standing silent", or refusing to plead, in which case the judge can enter a plea of not guilty on the defendant's behalf, so that the rest of the trial can happen. Turning that "not guilty" plea into a perjury charge would be a pretty gross 1A violation.

In the US and many other Western nations, the law operates on the presumption that the accused is innocent until proven guilty¹. To enter a plea as a defendant is to formally acknowledge charges filed in a court of law. A guilty plea simply indicates the defendant will not contest the charges, and the trial proceeds more or less directly to final adjudication and sentencing. Sometimes this is done as part of a plea deal where the prosecution and defense agree to a set of lesser charges, with reduced reduced jail times and/or larger fines. The defendant may noy even have committed any of the offences charged, but agrees to the to lesser charges to avoid time, expense or reputational harm of a lengthy trial.

A plea of not guilty simply indicates the defendant intends to challenge some or all of the charges, and is asserting their right to the presumption of innocence while the defense team reviews prosecutor's inculpatory evidence, prepares counterarguments and gathers exculpatory evidence.

The accused is presumed to be innocent unless and until a guilty verdict is reached on the basis of the evidence presented at trial. Additional charges of perjury would only apply where evidence is entered in bad faith, or if the defendant were to make false statements under oath.

1. In theory. In practice, we all know people get railroaded for any number of reasons, but that's beside the point.

In Hungary, no. Because you only commit perjury if you are under oath on the stand as a witness. You are not under oath simply defending yourself. As my lawyer said to me once: you can say or lie literally anything you just want.

Another thing to consider is just because someone says something that is not true based on reality, doesn't mean they lied. People's memories are terrible and easily manipulated.

This seems a very regional question.

No.

No, that would be an awful thing to do. You have to allow people to zealously defend themselves from any accusation. Also, in the US, the fifth amendment protects the citizens from being forced to testify against themselves. So punishing someone for pleading not guilty would directly violate the 5th amendment.

https://constitution.congress.gov/constitution/amendment-5/

No

If we assume US centrism here since you didn't specify country then practically you do get punished for pleasing not guilty. Not because it's illegal to lie but because if you plead guilty you usually get a shorter sentence.

I love this question.

Also it makes me so angry when serial killers still try to deny their murders years after the fact. The only thing worse than a killer is a lying killer.