The message is a constant string. Here's the relevant extract from my code :
//first i made the strings to be injected in the postdata area of the facebook url
name$ = "Record du défi mondial battu !"
desc$ = "C'est génial !"
//I made every required strings (with "https://www.facebook.com/dialog/feed?", obvisouly), but for shortness I'll skip them.
url$ = url$ + "&name=" + HTTPEncode(name$)
url$ = url$ + "&description=" + HTTPEncode(desc$)
openbrower(url$)
In the end, the message is successfully posted when I send it from my PC. But when using Android, every special character is messed up.