Chouby on "Polylang changes urls: how to avoid/disable automatic redirect?"

- have polylang do nothing in frontend: I'll manually query translations by myself.

Obviously, that's not something I forecasted ;-)

I mean: is it still fine for backoffice?

Yes. Frontend and backoffice are totally separated.

Can I still manually query what I need?

Not sure. It depends on how you use WordPress on frontend.

- to stop auto redirect, is there any other better way that doesn't imply core code hacking?

perhaps http://polylang.wordpress.com/documentation/documentation-for-developers/filter-reference/#pll_redirect_home