I did exactly what you're planning. I went home in 2006 after four years in Thailand, and got qualified in primary education. If you're dead set on one of the schools you named above then I would check that they actually teach French and Italian. I think you are right when you say that they may be too subject specific. It could work both ways though. From my reading of it, and having just gone through the whole process of applying for jobs, there are roughly 100 applications for every primary post advertised. While there may be less MFL jobs, there are less MFL teachers.
Your plan to get coaching badges is a good one, it is something I wish I had done. You need to make sure your cv stands out from the crowd and extra-curricular activities are a big thing in the international schools. Competition to get into Harrow, ISB and Bangkok Patana is fierce, and two years post qualification experience is the absolute minimum.
One other thing i'd do if I was you would be to start to collate a teaching portfolio as soon as you start your PGCE. Put in examples of lesson plans and children's work, photos of displays and happy smiling children. There are some good articles on the TES website about this. I'd also keep any nice thank you letters you get from parents or pupils.
The whole thing has worked out well for me though. I heading back to thailand in four weeks, start my new job in August.