Your DH should have read the email, but given it was you and not him in correspondence about languages, I think you can feel a bit annoyed that having already clearly expressed your preference for French, that info didn't reach the relevant person and get taken into account.
I think you could let the school know you feel this and remind them of the dates and different correspondences that you had about fRench before the German email went to your DH. At this point, Inwould also request that your email address is also added to any correspondence lists the school uses - ask for confirmation that this has been done too - should avoid this kind of thing in future.
That said, it is now too late and either friends or French because the allocations have been made. If French important then do the swap which has been offered. Actually, if he had been given French as you wanted, he might not have been with the friends anyway.
So, the school has not really been remiss here, except whoever corresponded with you didn't pass your communication to timetabler, but given an email was sent given a chance to object to the allocation and the timetabler and person you corresponded with won't have been the same person, and we are talking about a large organisation, where everyone doesn't know everything, they weren't remiss.
Lesson to learn here - copy absolutely everyone into every correspondence and at the end of every message always include the line 'please can you make sure that this email is forwarded to anyone who is relevant at the moment or might be relevant in future about this' and state the kind of roles which might be relevant,much as timetabler, Head of year, Head of Dept etc.
You've been unfortunate that this has happened, but it wasn't the schools fault and the timescales just mean he can't have the language and tutor group he wants and you will have to choose - but you have been given the choice to move, which many schools wouldn't make...so now you have onto decide how important the French is, because it is still available!