Q: What's the point of issuing an arrest warrant for Putin given that the chances of him getting arrested are effectively zero?

Aikhenvald (2004: 43) classes the Quechua language family as having a B1 Evidential system, meaning there are three evidential distinctions: direct (visual), reported, and inferred.
Direct, represented by -mi is used to indicate that the speaker was an eyewitness to the event specified.
Reported, or indirect -shi is taken to mean hearsay or secondhand information, or that the speaker is removed from the source of the information.
The final evidential, the inferential -cha, can invoke a sense of any of the following: probability, doubt, and uncertainty. This is usually translated as “probably” or “perhaps”.

У мові кечуа (Еквадор) відзначається Система Свідчення виду B1, тобто, граматика містить три принципово різні граматичні класи свідчення: прямий (свідок), почутий, та висновковий.
Прямий позначається суфіксом /-мі/ і вживається для позначення дії, свідком якої співрозмовник був особисто і безпосередньо.
Почутий або непрямий /-ші/ використовується для позначення чуток або почутої від когось інформації, або якщо співрозмовник був віддалений від джерела інформації.
Третій, висновковий /-ча/ позначає відчуття одного з наступного: можливість, сумнів або невпевненість. При перекладі зазвичай перекладають як «можливо» або «ймовірно».

So as of my writing of this question—November 26, 2018—Ukraine declared martial law after a Russian naval attack. And as per The New York Times:

Ukraine’s Parliament voted Monday to declare martial law in areas bordering Russia, responding to an attack a day earlier by Russian forces who fired on and impounded three Ukrainian naval vessels, leaving several sailors wounded.

My question is simple: What is the benefit of Ukraine’s government doing this?

• Is it to suppress a Russian-backed uprising in Ukraine?
• Is it an excuse to assert sentient, non-Russian influenced power in a region where Russian rule over Ukraine independence has been a constant sticking point?
• Is it something else entirely?

TL;DR: Ukraine is a Parliamentary-Presidential republic.
On the other hand, the President is the commander-in-chief of the country's Armed Forces.
This introduces a natural delay in the chain of commandment in case of a sudden aggravation of the situation.
The primary goal of martial law is to eliminate this delay, allowing the immediate armed response.

Also, it is internationally recognized act of war, so according to most country's Constitutions and Laws, an act of war should (must) be met with martial response.

На цій картинці диктатор Дутерте
ніби каже американському диктатору:
„You are next!“

Could Duterte run for US president? Is he a U.S. citizen?

After seeing a meme about President Duterte wanting to give away free guns, and his rather unorthodox ways of getting rid of drug dealers and communists; I came to wonder would there be anything in law forbidding him from running in the USA?

After all the Philippines got their independence in 1946 and he was born in 1945 which I believe implies he is a U.S. citizen.

If he is a U.S. citizen could the country theoretically call him up for aforementioned unorthodox techniques?

Stack Exchange sites should use official toponyms, accepted by the United Nations (UNGEGN). Any other naming would inevitably become disputed.

Moreover, a misleading spelling at a Travel site can lead the travelers straight into the trouble.

The other answer suggests to use Wikipedia, but open sources have some natural drawbacks that virtually eliminate the possibility to use them in official context — the only context which makes Stack Exchange a source of quality content, unlike forums, blogs, and other Q&A sites.

One vivid example is the disgraceful situation coming up around the Wikipedia page for Kyiv, the capital of Ukraine.
The United Nations (UNGEGN) has accepted the only possible English-language transliteration, Kyiv. There is no "or", "a.k.a.", or "alias" here.
However, the Wikipedia page has a detractive name "Kiev" which has its roots in centuries of Russian occupation and forced russification. There have been a whopping 9 (nine!) attempts to rename it, and, to the shame of the Wikipedia community, none were successful.

In the light of numerous accusations of a certain country committing a massive number of cyberterrorist acts in the recent years, successfully penetrating the most protected sites like presidential elections and national referendums, it is not surprising that the same force could easily penetrate the less-protected community-driven sites like Wikipedia.

And now it is on the way to penetrate the Stack Exchange, too.

There are good thoughts posted in comments above, I'll take my liberty to put it into this post:

• Since Stackexchange is an English-language website hosted in America, shouldn't we use whatever is the official name accepted by the US government? – JonathanReez
• The Kiev/Kyiv question is clearly resolved on the embassy website, for example: https://www.usembassy.gov/ukraine/ – JonathanReez

We do not force the users to obey this rule in their posts because it's impossible to enforce, but the site itself should follow the internationally-accepted (the UN) convention of spelling toponyms. This includes keeping the proper spelling of tags, UI (dropdown selectors), etc. This would make Stack Exchange a source of quality content, helping people learn, and avoid any misleading content.

Context (highlight mine):

But House Intelligence Committee Chairman Devin Nunes (R-Calif.), one of Trump’s leading allies on the Hill, privately urged Republican colleagues Tuesday to consider holding Rosenstein and FBI Director Christopher A. Wray in contempt of Congress if the Justice Department does not provide him with documents he has sought about the Russia probe in coming days.

[…] Nunes has also spoken in the past week with members of the conservative House Freedom Caucus, which has been supportive of Trump, about how a potential contempt effort could unfold. He has not yet spoken with House Speaker Paul D. Ryan (R-Wis.) about possibly moving forward, the two people said. — The Washington Post

In my naive understanding, the close allies of a subject¹ of a criminal probe are trying to get access to temporary documents that contain facts that the investigation has already established (and — most importantly — what has not been established yet).

These allies submit an official Congress inquiry to the DOJ, or else they threaten to accuse the DOJ of contempt of Congress.

Most obviously, since these Congressmen are "leading allies" and "been supportive" of the subject, they can be tempted to disclose the materials to the subject of the investigation. Which, in turn, would let him hide evidence, build up the defense strategy, threaten the witnesses, and so on.

Question: Is there any provision that regulates some kind of Non-Disclosure agreement to be signed by those who submit such demands? If so, how is the possible violation being prosecuted?

I am aware of the recent move of Rosenstein who refers to a similar case when in 1941, when Attorney General Robert Jackson investigated a corruption scandal in the US Navy. He refused Congressman Carl Vinson's demand to disclose the documents of the investigation, arguing, among other things, the possibility of disclosure to the enemies:

Second, disclosing certain investigative reports would give aid to our enemies and jeopardize our national security.

This makes me thinking that in 1941, there was no regulation of non-disclosure. So, have any been adopted since then?

¹) subject, not a target;

According to The Guardian, President Trump was subject to criticism over his decision to congratulate President Putin on winning Russian elections in 2018:

Donald Trump defended himself against criticism over his congratulatory phone call to Vladimir Putin following the Russian president’s recent re-election, insisting on Wednesday afternoon it was in US interests to maintain a positive rapport with Moscow.

AFAIK, congratulating a President for winning the elections is typically an automatic diplomatic gesture that is performed throughout the world and it happened before even for US–Russia (source):

• "former president Barack Obama also wished Putin well after the Russian election on March 4, 2012"
• "Former president George W. Bush also called Dmitry Medvedev in 2008"

Another example is a Romanian President who did a similar gesture, and Romania–Russia relations are not exactly full of unicorns and rainbows (also this source).

Question: Why was President Trump congratulating Putin on winning the election heavily criticized?

Because the very elections are disputed, and congratulating Putin on winning these elections is a semi-official recognition of these elections.

In 2014, Russia has committed an armed invasion, military occupation, and subsequent attempted annexation of Crimea.
The vast majority of the world countries neither accept nor acknowledge the Russian sovereignty over Crimea. The US repeatedly condemn the occupation, too.
The 2018 elections were held in Crimea.
Hence, the legitimacy of Putin's presidency is disputed.
The White House national security team reportedly warned Trump, literally written in capital letters, "DO NOT CONGRATULATE".

Therefore, the criticism is based on the following reasons:

1. The legitimacy of Putin as a president is disputed. Any kind of diplomatic action should be carefully considered before the national security team can elaborate an adequate response.
2. Trump had gone against the advice of his own team, which indicates a deep schism even among the top WH officers.
3. This also makes stronger the argument of those who accuse Trump of The Collusion, and the accusations are now harder to deny;
4. The arguments about 2012 do not apply, as shown in existing answers to this question.

• Why is “president for life” in China such a big deal?
• Why are states purportedly performing assassinations with chemical and radioactive weapons?
• What would the Kremlin stand to gain from killing the ex-spy Sergey Skripal?
• Are there any facts according to which the Russian government is responsible for the chemical attack in Great Britain?
• How does the expelling of diplomats work to create pressure on the diplomats' home country?

• Why can't the purported assassination attempt on the former Russian spy Sergei Skripal be a false flag operation?

"Great Leap Backward" was the title announcing the term limit removal in China. This BBC article tells us more about this:

The constitution has been altered to allow Xi Jinping to remain as president beyond two terms and they would not have gone to this much trouble if that was not exactly what he intended to do.

I am wondering why it is this so important.

[…]

Question: Why "president for life" in China is such a big deal?

Why "president for life" in China is such a big deal?

— Because the increasing shift towards a dictatorship state¹ may trigger a chain of uncontrolled events that, in turn, would undermine the Western investments and the international trade.