you can do
editor.commands.bindKey("some-key", "startAutocomplete")
editor.commands.bindKey("ctrl-space", null) // do nothing on ctrl-space
btw to which key do you want to remap it?
ace opens autocomplete popup on "Ctrl-Space|Ctrl-Shift-Space|Alt-Space"
https://github.com/ajaxorg/ace/blob/master/lib/ace/autocomplete.js#L278
are all of these unavailable on Chinese Windows.