**Most likely they'll just close their ML departments. Students of lots of other academic disciplines choose to do optional years abroad
Anecdotally, this was DD's experience this year - very few international students across 2 countries studying MFL, more business related subjects with JH language or elective language modules added onto their core studies.
@Michele09 I will leave others to comment on their own or DCs' respective experiences of universities, other than to say the usual suspects do JH - UCL, KCL, Manchester, Birmingham, Edinburgh, Exeter, Loughborough, York, Durham, Edinburgh, St Andrews, I think still Glasgow as well as Oxbridge as well as more in the full tier spectrum (subject to continuous cuts). If your DD's more adventurous, she could also consider Ireland which would at least overcome the hurdle of Erasmus accessibility, though hopefully that will also be set to change from UK UG students soon. Just work out her A levels/IB predicted against the rough number of points needed for the Irish system (CAO site has all the info).
All courses will differ. Over her sixth form, your DD should work out what's important to her in a study programme. Some will focus more on language acquisition, less on the history, cultural, literature, politics etc, or vsv. Some will be more flexible on module choices to align with the student's interests, others will have core which could include dry, less interesting stuff (all subjective!).
In our case, the YA was the most important factor for DD, the total immersion including being taught in target language to offset her starting her ab initio language later in Y2. Her feedback was that the Edinburgh, St Andrews, Durham etc students' Arabic language skills were more advanced, but they had less overall ME regional knowledge across the wider modules, which was primary as part of her multi disciplinary programme (vs straight JH). It made sense, 6 hours language hours vs her 2 per week. But it was a conscious choice and she caught up in all but speaking she thinks. Her Spanish was conversely more advanced, more down to her having invested acquisition to include business Spanish through work opportunities. She aims to use her Spanish post studies, not all MFL have this desire.
Many European universities study late into the summer. Students in Istanbul were sitting their exams over xmas period! So double check the schedules if she needs to be back home for summer/internships etc.
Final point from me on this thread for prospective students is that even studying in an Erasmus university, the only upside is the relationships gained from all the partner universities, which I would suggest she researches as part of her shortlisting. The downside is that apart from sign off on study/activity for YA, the onus is pretty much on the student to source the accommodation and check the appropriateness of course, take the necessary language tests, find room mates, work out visa requirements, translate requirements off websites etc. This thread shows that you do not rely on the home university's communications, it's also often out of date. DD's small course has had her peers attend universities in Middle East, Morocco, Istanbul, Germany, Austria, Italy and France and ONLY DD's Cairo accom was university aligned assigning her a female only apartment. She found her own comms with dept ahead of departure so shitty she arranged a zoom call for all the Y2's choosing their options as a FAQ session.
Good luck, hope this thread hasn't put off another language UG hopeful :)