1. Log in as admin and go to Control Panel/Instance Settings/Localization.
2. Add Slovak to the available languages, then set it as the default instance language.
3. Create a new blank site (it will have Slovak as its default locale).
4. Go to Documents and Media in that site and create a new Document Type on which you put a Decimal field.
5. Create a new document of that type, type in 3000000,33 (3 million comma 33) in the decimal field. Publish.
6. Reopen the document for editing.
Result: Note that the number appears now with delimiter spaces (3 000 000,33). If you click Publish, you get an error to provide a valid number. You have to remove the spaces in order to be able to publish your modification.