I just committed a change to mojoPortal trunk that may be a workaround for this at least for english. I added the english text to the buttons declaratively. So it should at least show the english text on the buttons until this is fixed in Mono, it just won't localize correctly until then.
Seems like this was fixed in Mono at one time and has regressed. I'll have to try and find the old bugzilla and re-open it.
Hope it helps,