If you “just want to display English everywhere” then the easiest option that I’ve tested is to just add a few lines to the lua file that it uses to do something like:

if ( keyvalues["name:en"] ~= nil ) then
   keyvalues["name"] = keyvalues["name:en"]
end

If you want something a bit more complicated, like display one language in one area and another in another, then you do that by following the procedure at https://www.openstreetmap.org/user/SomeoneElse/diary/42069 .

With either method, you’ll get English names if the exist and whatever’s in the “name” tag if they don’t.