Overview of the Issue
When you use Password Protect WordPress to protect a page or a post with a password, its translations are not protected.
Password Protect WordPress saves the password on the original page only. The translated pages have no password, so a visitor who opens a translated page sees its content without the password form.
Workaround
Until Password Protect WordPress fixes this issue, protect each translation too:
- Go to Pages and switch to the language of the translation.
- Click Protect on the translated page.
- Set the same password as on the original page.
Do the same for posts. Repeat this each time you change the password of the original page.