She came to UK when she was about 15 or 16 so still mainly grew up in Chile really. Personally I lay the blame squarely at her feet, she never spoke to her kids in Spanish at all growing up. Massive waste of an opportunity - and seemingly paying for it now!
I think it was pretty unnecessary for the new Chile manager to come out and say that really, especially when he won't have even met the bloke, never mind seen him with the squad. The stuff about team spirit doesn't make much sense when you consider the players and fans have loved him since he's been with Chile, his impact has only ever been positive in that regard. To me it smacks of a new boss in town singling out a popular player to make an example of. It may be a bit of a miscalculation, a lot of fans won't be happy he's been left out.
Regarding learning the language, to offer something of a defence of him, it can be quite hard to get opportunities to practise a language when you're an English-speaker, because everywhere you go there will be people who speak at least a bit of your own language, and are keen to practise themselves. I suspect that will be the case in the Chile squad, there will be a core of players who speak a reasonable bit of English who he's fallen in with, and his attempts to interact in Spanish will be reduced to a bit of a novelty on the bus or in the pub, rather than any meaningful everyday communication. I'm sure he's been taking classes but that alone can be very slow-going in terms of getting up to speed with real-time spoken interaction. For anyone saying they've got up to an "intermediate level" on duolingo, I'd like to see you go and interact in real time with a big group of working-class lads speaking at a hundred miles an hour, using all sorts of slang and niche football terminology etc. I've spoken (Chilean) Spanish to a very high level for at least 15 years and even I get lost quite easily - following that kind of language as a learner is near impossible.
But again, all his mum's fault really!