Why does Claroline display messages in my language but sometimes in English ?
From ClarolineDoc
English is chosen as the default language in Claroline when a translation is not present.
New tools or new features are sometimes not translated yet in other languages. This might explain, for example, on a Spanish course page, why some tools appear in English instead of Spanish.
The solution in this case is to translate the missing files from English in the /lang/english repository and put them in the /lang/my_language repository.
Any help for translation is also welcome for further versions. Don't hesitate to contact the Claroline team : info@claroline.net.

