The language files will not be updated by updates.
Only the file ./cmsimple/languages/default.php will be updated, newly introduced language variables appear in English in all languages and can be translated in the backend. However, you can also update the language files en.php and de.php manually.
You will find the files en.php and de.php in the folder ./setup/defaults/ of the download, upload the two files to the folder ./cmsimple/languages/ to update the language files manually.
At the moment en and de are included in the CMSimple download.
Translations are welcome.