Hi Tomas,
Unfortunately, yes, that is by design currently. AtoM is designed to be a multilingual application, so users can add content in different languages. Most fields in the database, including the static pages, are split into i18n tables (which is developer-speak for internationalization), so you can add different content for each culture in use.
If you are using AtoM in a monolingual site, there are a couple things you could do to improve the end user experience however.
First, you can navigate to
Admin > Settings > i18n languages, and remove every language expect the default installation culture of your site. You should
reindex your site after doing so. See:
Additionally, you can hide the entire language menu from view, via Admin > Settings > Default page elements. See:
Doing so should prevent users and bots from stumbling across the other page versions.
I hope that helps!
Regards,