I can't say I'm familiar with languagede-DEde-DE.mod_footer.ini.
If you're editing the text in the admin area of Joomla with a wysiwyg you should have an option under the 'styles' drop down for 'small' text.
Other wise if you can edit the source code for the module text you can add the style attribute to any html tag this would look like
style="font-size: 12px;"
<span style="font-size: 8px;">footer text</span>
or
<p style="font-size: 8px;">footer text</p>
adjust the number to suit your site. Let me know if that helps.
