WordPress Translation to french, at -> à not working

Question

I have a german / french blog. I installed the german WordPress version, so I already had de_DE.mo and de_DE.po in wp-content/languages. After I realized that the content of a comment's <time>-element wasn't translated, I googled and downloaded fr_FR.mo and fr_FR.po and put them in wp-content/languages. Now everything I tested works, except that 'at' doesn't get translated to 'à' ( I get: 3. février 2013 at 17:00).

So I opened fr_FR.po to see whether there is a translation available. I found this:

#. translators: 1: date, 2: time
#: wp-includes/comment-template.php:1367
msgid "%1$s at %2$s"
msgstr "%1$s à %2$s"

Which seems alright to me. So to make sure, I replaced the existing mo file with this. Still it does not work.

How do I make it translate 'at' to 'à'?

I'm using WPML.