If you want to have the static-text-output in other languages than default (english), you have to do following steps:
- activate your locale with raspi-config, it must not be default
- restart your webserver for loading new locale-configuration
- set your locale within setup.php
To be a part of the translators-community, feel free to copy an existing locale-tree within the locale-directory to your own locale, modify the settings.php-file within this directory and modify the messages.po within the LC_MESSAGES-directory. After this, you should generate a messages.mo with the command 'msgfmt messages.po -o messages.mo'. The command is part of the gettext-package to be installed before with 'apt-get install gettext'.
To get the translations for DataTables, take a look at https://datatables.net/plug-ins/i18n/ - here you'll find links to translations you can copy&paste into settings.php of the locale-directory.