I think, but stand corrected if people disagree, that language teaching tends to begin too late. I say that because I learned my 'second' language from when I learned to speak through my day carer. Neither of my parents learned more than a few words of German ever. So I was hearing German from something like 16 weeks old. I used a Ripuarian dialect, a version of Kölsch, but was taught Hochdeutsch through pre-school and the year and a half of primary school before moving to England. I continued to use it because when my father was demobilised, several other members of his unit where allocated housing in the same newly built block of flats as us. Some mothers were German and those children spoke German indoors and in their homes I continued to do so. Thus from when I left home to go to study until when I began postgrad research that I by coincidence rather than intent did within a Berlin based research group, was three or four years. During that time I used German texts which are prolific in the social sciences to my benefit.
However, having chosen to do my research in Peru I had to learn Spanish. The penny soon dropped for me that it was rather like the French and Latin I had learned for six years at school and very much like the Corsican dialect of my very 'temporary' first wife. Of course, working in migrant communities and the Andes I also had to learn Quechua of the Ancash-Huailas dialect variety.
Since then I have learned other languages including my wife's Ticinese Italian, Portuguese, Kinh (principal language of Viet Nam). My observation is that on the one hand it gets harder learning as we get older which includes harder at 22 than 2, that we also forget a certain amount of language as even now I have not recovered the French I once had and both my Englsih and German are suffering a bit.
What is different is that I have not formally studied most languages I know and whilst I have good school qualifications by some fluke I failed 'O' level English three times although I have English literature at that level and by a bit of twisting rules have 'A' level English, sure I have Latin and French at 'O' and German and German Literature at 'A' level, but nothing of a standard that enables me to teach. I did a bit in Peru, but more by bluff and bluster. I have met gifted language teachers but also plenty of people who 'boast' their superior degree who I scarce understand in conversation, dread to think what a classroom would be like. Emma, like most multi-linguists, and amongst anthropologists there is of need a fair few of us, makes heck of a lot of sense. So too does Sylvie. Andrew, well I know his commitment well enough. The problem is that there are too many people unlike you three and more like me who assume that because they speak X they can teach it. Without the nuances of language it does not work, grammar is a tough one to begin with because there is no 'perfect' language in creation. I do reviewing and editing for journals and see that as often from language 'natives' as 'foreign users' in the couple of languages I review to begin with.
However, as I have already said, the language course trips are 'business' and have any of us ever heard of a business with a conscience? Therein a big problem, discuss that and suggest a solution if you can face the frustration that comes with it.