debconf-i18n software package provides full internationalization support for debconf, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install debconf-i18n
debconf-i18n is installed in your system.
Make ensure the debconf-i18n package were installed using the commands given below,
$ sudo dpkg-query -l | grep debconf-i18n *
You will get with debconf-i18n package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Language packs |
| Package | debconf-i18n |
| Version | 1.5.59 |
| Description | full internationalization support for debconf |
| Sub Section | Localization |