To solve this, I had to encode it:

function NotReleased(tcDate)
{
   alert("This video will be released in the week of "+tcDate+".")
}

function NotReleasedFrench(tcDate)
{
   alert("Cette vid\u00e9o sera disponible dans la semaine du "+tcDate+".")
}

I don't know if i ever included a French character as is in a .js file as this is usually processed from the application. Is there anyone else who succeeded to put directly the French character in a .js file?