Hi!
You have these choices:
http://my-site/projects/my-posts
http://my-site/projects/mes-articles
if you choose to set the language from the content
or
http://my-site/projects/my-posts
http://my-site/fr/projects/mes-articles
if you choose to set the language from the directory name
In any case, it is, for the moment, not possible to have the same slugs for two posts in different languages.