What does "people" mean in English language Constitutions?

The Japanese Constitution begins "We, the Japanese people,"

The Japanese Constitution uses the word "people" a lot in the official English translation where the official Japanese version says 国民 {kokumin} (Japanese national). I've heard conspiracy theories on the Internet that claimed that this was Japan's sneaky way of changing the Constitution from the unaware Occupying Forces who had a significant hand in designing and writing the Constitution by basing it on various Constitutions and legal documents of the world. (When Japan made its first Meiji Constitution, it also evaluated existing overseas supreme laws to craft its own first Constitution)

To make things more confusing, the Japanese language version of the Constitution occasionally translates "people" or "all people" more closely to 何人 {nanbito} (everyone).

Generally speaking, the high courts of Japan consider the Japanese language version of the Japanese Constitution to be the canon official version that they use to interpret the law.

So, does this mean that when the word "people" is used (in English or the equivalent Japanese) this means the Constitutional Article applies to non-nationals / foreigners as well?

The answer is: not necessarily.

Many English language constitutions from around the world use the word "People" (capitalized or not) to mean exclusively citizens / nationals.

For example, the United States constitution says this about voting rights:

• "The House of Representatives shall be composed of Members chosen every second Year by the People of the several States …"
• "The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; …"

When the United States talks about electing leaders to serve the entire nation, they do not mean minors, criminals, or non-citizens. Note that "people" is capitalized in one phrase and not in another; the capitalization does not imply citizen.

On the other hand, there are many parts of the U.S Constitution where the U.S. Supreme Court has ruled that the word "people" does indeed include non-citizens / non-nationals.

The word 国民 {kokumin} (Japanese national), however, when used in the Japanese Constitution or other laws, is not ambiguous: it means a person who possesses valid Japanese nationality (including naturalized persons).

Why do constitutions not talk about non-citizens?

Not many constitutions in the world talk about or specifically mention non-nationals or non-citizens. According the The Constitute Project's database of 180 constitutions from the world, only 62 mention "foreigners".

The primary reason for this is because the target audience for most constitutions is the people to whom the country belongs to; who has sovereignty. Many constitutions make this crystal clear in their opening preambles when they state that sovereign power resides with the People (as in national citizens). The is especially true with respect to constitutions that were born through warfare, when one group is defining who the land and power belong to: Japanese People / Nationals — as opposed to a monarch, colonial power, or foreign occupying force.

The Japanese Constitution makes it very clear who their Constitution is "for" in the first four characters of it: 日本国民 {Nippon kokumin} (Japanese national) is translated in the English version as:

"We, the Japanese people, …"

This doesn't mean that non-nationals in Japan have no human rights; Japan's constitution contains Article 98 says:

This Constitution shall be the supreme law of the nation and no law, ordinance, imperial prescript or their act of government, or part thereof, contrary to the provisions hereof, shall have legal force or validity. 

The treaties concluded by Japan and established laws of nations shall be faithfully observed.

この憲法は、国の最高法規であつて、その条規に反する法律、命令、詔勅及び国務に関するその他の行為の全部又は一部は、その効力を有しない。  

日本国が締結した条約及び確立された国際法規は、これを誠実に遵守することを必要とする。

The second paragraph ensures that when Japan signs treaties and conventions at the United Nations or with other countries, it is constitutionally bound, by its supreme law, to obey them. For example, Article 98 was used to enforce the UN Convention of the ICERD for the case of Ana Bortz. Ana Bortz was able to win her lawsuit for racial discrimination because of Article 98 and not because of Article 14, which limits the right to 国民 {kokumin} (Japanese national) in Japanese even though the English version says "All of the people …".

All of the people are equal under the law and there shall be no discrimination in political, economic or social relations because of race, creed, sex, social status or family origin.

すべて国民は、法の下に平等であつて、人種、信条、性別、社会的身分又は門地により、政治的、経済的又は社会的関係において、差別されない。