It does only allow filtering by one language at a time, but you can build your hotbar of the stations you like that you find across any filters.
The scan works on the displayed results. If you change the filter, it starts with the new list -- but all the results are saved regardless.
Hope that makes it a bit bitter!
Really great site though!
Quick suggestion: let us resize the channel browser when it's horizontal, and perhaps allow collapsing it altogether
When your window is wide enough (on desktop), you should be able to drag the split point between the TV display and the channel list.