Comment 2 for bug 961741

I did some more testing.

1. I tested with Unity 5.8 (latest updates applied and rebooted)
2. I updated the summary of the report to reflect the new information.
3. The source of the bug appears to be the bad control of the keyboard state.
Specifically,

a. If the dead key is on a single key (instead of having to press AltGr + key to get the dead key),
then it works. You can type áááá just find. Such is the case with US International with dead keys, with the dead key is on '.
However...

b. If you press by accident the dead key twice, then you can no longer type dead keys. You need to press Esc to get the input go away, then bring back up Dash or Lens. You get something like ááá´´a´a´a
That is, when you press the dead key twice, Unity did not expect it and does not obey dead keys anymore. There must be some flag set, that makes Dash/Lens to think that the dead key is already active, so no new dead key can get through.

c. If your keyboard layout requires to press AltGr + somekey in order to get the dead key (such as GB layout, or GR layout), then the fact that you press the two keys in order to get a deadkey, makes Dash/Lens to exhibit the bug straight away. So you get 'α'α'α'α.