This is a more focused follow up to a question I had the other day about moving to other countries. I'm wondering what the best options are for learning a new language at the moment. I'm vaguely aware of companies like Duo-lingo losing their reputation lately and it's hard to trust the top google results nowadays with all the SEO junk. So does anyone have suggestions for trustworthy/useful sites for learning a new language? If it matters, in particular I'm interested in trying (In roughly this order) Vietnamese, Chinese, Japanese, or Spanish.