Update i18n/ja.toml

**This is a...**
- [x] Feature Request
- [ ] Bug Report

**Problem:**

Outdated content `i18n/ja.toml`.

```
i18n/en.toml 54 insertion(+)
```

**Proposed Solution:**

Update content `i18n/ja.toml`.

For details, please execute the following command.

```
git diff 551489f 7b07d19 -- i18n/en.toml
```

And please submit this pull request directly to master.