Are Satanists legal in the US? I heard that Satanists in USA are legal and are even represented in the counsil of the churches and have "study books" used in school. In Russia there is a law that acts which are done to harm somebody other are illegal. Does the US have a similar law? If so, would the courts consider Satanism harmful and thus illegal (based on the fact that Satan's purpose as he is described in certain religions is to harm and the purpose of Satanists may be to follow Satan as described in certain religion)?
There is no such law in the US, although there many laws prohibiting specific forms of harm, for example laws against murder, theft, assault, arson. All laws are predicated on the idea that an illegal act causes harm, but I don't get to deem, for example, that you are harming society by opposing Satan. There are no laws prohibiting any belief in the US, and such a law would be unconstitutional (in violation of the First Amendment). So being a Satanist could not possibly be illegal.
It is illegal in Morocco to possess or distribute pornographic material of any kind. This includes nudes of the hypothetical Vietnamese girl.
It is legal to be wrong, it is legal to say false things in public (leaving out defamation), and it is legal to buy and manufacture signs that say false things. Moreover, the sign does not make a false statement, in that legal liability is distinct from moral responsibility. In fact, the sign helps to decrease their legal liability. Via this sign, you have been put on notice that the truck may spray a bit of gravel, so by following too closely, you are negligently contributing to the damage. This is what also underlies those disclaimer signs with "not responsible for theft from your auto". There is nothing "official in appearance" about this sign (a legal citation of a statute might have such an appearance).
In the US it is not a crime to be in the country illegally. As a general rule, it is not a crime for a removable alien to remain in the United States. Arizona v US So it's illegal, you get a state induced consequence (deportation) but it doesn't make you a criminal e.g. you don't go to jail for it. I have no idea if that's what's going on over there but it's a plausible explanation.
If you cannot legally purchase a gun in Utah due to any restriction, such as residency, and you engage someone else to knowingly buy or gift you a gun (such as a "straw man" purchase from a dealer or private sale), that is illegal. From the same link you posted (my emphasis): Can I buy a firearm as a gift for someone? Yes, as long as the receiver is not a prohibited person and the gifting is not being used to circumvent a background check or other laws. Calling a purchase intended in place of another is a straw purchase.
You have misread the DMLP page. In Pennsylvania, it is illegal to record a conversation if you are a party and if the other party does not consent. The fact that federal law doesn't ban something doesn't mean that states can't ban it. There is generally a presumption that when both the feds and the states can legitimately regulate something, the feds weren't trying to preempt all state laws on the topic. While people often say "federal law takes precedence over state law," the normal rule is that both laws apply; the federal law only blocks the state law if the feds wanted to block said state laws. So far as I can tell, the federal law has never been held to preempt two-party consent laws; the point of the federal law was to restrict recording, not extend it. It's like how federal law doesn't prohibit taking hostages inside the US to coerce a private company into doing what you want (anti-terrorism laws might, I guess, but the federal hostage-taking law doesn't); while the federal law excludes most hostage-taking in the US, that doesn't mean that it's legal to take hostages. Congress sometimes wants to establish nationwide standards for something, but the presumption is that they didn't.
Questions about whether a certain action is "just" tend to be maters of opinion, politics and philosophy, but it can be addressed from the perspective of legal theory (especially following the model of common law, where legal principles are based on concepts of just and proper action). Whether or not a certain action is actually legal in a certain jurisdiction depends on the laws of that country -- I suspect that the answer is different for the US versus China. The first question would be whether those government officials have the legal authority – I assume they do. Such authority is generally governed by some specific circumstances, for example, "poses an imminent and grave threat to public health". It is basically not a legal question whether quarantining in the face of this viral threat is necessary from a public health perspective, that is a medical question. What the law would say is that if this is a serious threat, then a person's liberty can be curtailed to a limited extent, because a person does not have the right to harm others because they don't want to do some thing that protects the rights of others (be vaccinated, stay in quarantine until it is safe). However, principles of legal justice also say that the government's response should be proportionate, e.g. shoot-on-sight in response to a sneeze is not proportionate. Quarantining has long been recognized as a valid, just and legal response to such extreme medical threats. Historically speaking, quarantining used to be the only effective action that a government can take against e.g. smallpox, plague, Spanish flu, Ebola.
This is a hard question, but a good question. The following relates to the issue from the perspective of the USA. You ask "...if the US wants to invade France, can they officially declare war by...", You have to make clear what you mean by "can". If you mean whether or not the US has the physical ability to do this, then of course they do. If you mean whether they are allowed, then this is another question. When you ask whether something is allowed, then you have to make reference to a moral code or a law that determines what is and what isn't allowed (legal). Normally each country will have laws that govern what is and what isn't legal for it's citizens to do. That hard part is how this applies to nations. There are two sides to the question. (1) What are the leaders allowed to do under their own laws, (the domestic laws) (2) what are countries as entities allowed to do? (the international laws) It sounds a bit like you are asking about the second thing. Here treaties govern what is and what isn't "legal". However, usually when someone breaks a law, other entities have the power to enforce that law and decide (judge) whether the person has broken the law. The question is: who decides whether a country has broken a treaty or an international law? And if a law is broken, what exactly can be done about it? This is hard to answer. Consider for example the conflict in Ukraine. Here many will argue that Russia has piratically invaded Ukraine. There should be war between the nations. But Russia denies this and other world powers have done little beyond imposing sanctions. This illustrates how hard it is to deal with this question. One question that comes up is what the purpose of international treaties are if a country can just violate them without much consequence. Pointing out two points about this. (1) If, for example, a president wants to convince his/her own congress that the country should engage in war, then it makes a stronger point if you can show how the country you want to engage has violated international trities. (2) After you have won a war, you might want to prosecute the leaders of the loosing power. Here you will stand stronger if you can make references to some international law that existed before the conflict started. This second point is illustrated in the Nuremberg principles. Here it was exactly stated that "Any person who commits an act which constitutes a crime under international law is responsible therefore and liable to punishment." According to the US constitution "Congress shall have power to ... declare War". That means that historically Congress has the power to decide where to wage war. The War Powers Resolution says, for example, that "The President in every possible instance shall consult with Congress before introducing United States Armed Forces into hostilities ...". Note that this doesn't mean that the US has do formally declare war before going to war. Example: The Iraq War was authorized by Congress, but there never was a formal declaration of war. It is interesting that you ask about the timing for when the declaration should be given. The Japanese wanted to deliver their declaration of war just before the attack on Pearl Harbor. But because of issues with decrypting the message from Japan to the Japanese Embassy, the declaration wasn't delivered until after the attack. Remember also in all of this that the winning party to a conflict, usually decides what was and wasn't legal! One good reference for more on all of this is the report by the Congressional Research Service called "Declarations of War and Authorizations for the Use of Military Force: Historical Background and Legal Implications". Here you can see more on what I have tried (and failed?) to say above.