Any question answered...

The best way is to go and live there, which is cheaper than living in London.

The second best way is to have some reason to have to learn it, like being able to communicate with a partner, children, friends, or business contacts.

I find that if you make it a hobby, you'll never properly do it.

With the apps you'll probably get quite good at passing each level, but if you don't actually use it you'll never internalise it.