Language selector - drop-down - Next to the text field, it is displayed when there are several languages installed (disabled languages are displayed in the drop-down). It allows choosing in which language the content of the field.
By default, if the input text is mandatory, then only the default language is expected to be fulfilled.
If the input is displayed in the Front-Office and only the default language is fulfilled, then Front-Office displays for the other languages the text from the default language.
If the input text is mandatory for all the languages or just the default language, then It must be warned in the message which language is problematic.