Tokyo dDistrict cCourt has summoned Kim Jong Un, the supreme leader of North Korea, because he hais beening sued in Japan.

Unless the suit is already over, in which case the sentence should be:
"Tokyo District Court summoned Kim Jong Un, the supreme leader of North Korea, because he was being sued in Japan."

Five Japanese people claimed they were deceived in the repatriation program by pretending North Korea was the paradise on earth and they're forced to live tough days.

In general if the nationality ends in -an you don't add "people": Korean, German, American
If the nationality ends in -ese or -ic you add "people": Japanese, Chinese, Lebanese, Icelandic, Gaelic
Greek, Swede, Dane, Finn don't need "people"
French, Swiss do need "people" (or you can change French to Frenchman)

According to customary international law, countries can't be a defendants, but Japan doesn't approvrecognise North Korea as a country.

recognize if you follow American conventions.

Thus, they could bring the actionsue them.

I'm sure Kim Jong Un won't come to the court, but it's would be funny if he comes.

or: I'm sure Kim Jong Un won't come to court, but it would be funny if he does.

The Tokyo dDistrict cCourt has summoned Kim Jong Un, the supreme leader of North Korea, because he hais beening sued in Japan.

Five Japanese people claimed they were deceived in theby a repatriation program bythat pretendinged North Korea was thea paradise on earth and they're forced to livforced them to endure tough days.

Instead of tough days, I might write "poverty," "hardship," or be more specific about what their experience was like.