In the download you will find a folder "2lang", that you can copy and rename according to the language (en, de ...) and upload it into the installation folder of CMSimple.
If the function languagemenu() is included in your template, and the corresponding flag in the flags folder exists, a small flag will appear in the appropriate place.
flags folder: ./userfiles/images/flags/
Calling the language menu in the template:
<?php echo languagemenu();?>
Now you have to set the necessary read and write permissions for a few folders and files.
"xy" is an example for de, en, fr etc.
Folders: chmod 777
Files: chmod 666
Now the second language should work and can (and should) be configured.
Under "Settings => CMS => Language => default" must be defined the main language by a select box, for a properly working languagemenu.
The default language is the language of the main site or the parent subsite, and not the language of the current second language, which is recognized by CMSimple itself.