Diacritics not replaced in the url

Hi,

I`m new to drupal I`ll try to migrate from joomla 1.5 to drupal 6.
Curently I use acquia drupal with drupal 6.11.
The problem is that caracters with diacritics are not replaced by the caracters that should replace them. For example "ă" is not replaced with "a" in the url. I cleared the cache, deleted the aliases but nothing.
I renamed "i18n-ascii.example.txt" to "i18n-ascii.txt" but nothing.
Shoul I install "http://drupal.org/project/i18n" ?

Thanks