Hi Geraldine,
So, meanwhile just jumped in what would be most cost efficient implementation for the HREFLANG on your website.
Give the following article to your developer: https://support.google.com/webmasters/answer/2620865?hl=en
Basically he will create a sitemap for each of the websites, which will indicate what is the alternate version of every single page in other languages.
You will then submit this sitemap to EACH of the Google Webmaster Tools accounts for the websites (.fr, .de, .com, etc.)
This should be the fastest and most cost efficient in your case.
Reminder: Remove the Hreflang link from current versions. It is the best to indicate alternate via only once channel.
Gr., Keszi
(almost forget about this version)