Problem solved.
Thank you all the same.
I am currently creating a plugin and I would like to know if I can add a translation even if the site is not multilanguage.
Ex:
Config (for default language) :
c::set('myplugin.language', 'en');
Languages files :
plugins/
myplugin/
languages/
en.php
de.php
fr.php
My plugin is finished soon, I just have this little detail to settle.
Thanks!