I don't use Midnight Commander (mc) or bmon at all, but I took a look at them.
Basically with Putty, I have Window > Translation > Character set received set to UTF-8. Then during my Putty session, envvars are set to TERM=xterm-256color and LANG=en_US.UTF-8, and mc looks correct with line characters. It even works with the mouse, wow! However, bmon has the "lqqqqqk" display problem.
I then installed ncurses-term for the TERM=vt-utf8, and then ran bmon as env TERM=vt-utf8 bmon, and the display looks a bit better with line art. There is some small problem with the close dialog box, though.
I suggest shell aliasing or wrapping your bmon as env TERM=vt-utf8 bmon and leaving your LANG set to humanlang.UTF-8 alone.