Hey OP – MFL specialist here.
A few thoughts – yes the format of the exams (assuming the same board, most likely AQA, but I would check they are the same board at DC’s school) will be identical; the topics covered are basically the same; the things you need to do (opinions and reasons, x number of verbs used, extension of your answer in xyz way, reading an original text from a German or French fairytale) will be the same for French and for German.
They are very different languages but for some that is an advantage as you are unlikely to get them confused. OTOH the way (for example) the perfect tense is formed is very similar in both (even the use of verb to have vs verb to be) so that is helpful.
I think it’s great that he wants to take two languages – so few people do this and if he wants to go on to do two at A level well wowser, excellent and something that will surely give him an advantage in the jobs market going forward.
Are they harder subjects? I mean a lot of schools insist that all or most students take a language and often they do not like it and do not enjoy it and do not do very well, which will surely skew the figures. DS2 had to take MFL and a lot of his mates got a 2 or a 3 when the rest of their grades were 5/6 and above. Not sure that necessarily means MFL is harder. But of course the students also had to take geog or history and the same thing didn’t happen there.
In terms of percentages – I checked a few AQA 2019 grade boundaries and a 9 in Eng Lit required 88%; in drama 86%; in French or German, 83% and in geography oooo just 73%. So that feels middlish to me.
I agree with a PP that I would never predict a 9 for MFL – why would you? An 8 is a great grade. I also agree that MFL requires study and earning from yr 7 – you cannot cram knowledge of verbs and vocab into a few weeks in the way that you could, perhaps, with English texts or history topics. Maybe that’s why they are seen as challenging? But if your ds is on top of this and getting goo