"Just as a side note, running the repair ends with the Failed to load language dll error."
It may be time to do a clean install of Avast:
Clean Install of Avast:
https://goo.gl/4Ptzkf
This was a clean install.
You mentioned repair
Correct, repair is what has been instructed by drake127 and I am reporting that the Repair produces this error.
Due to the issues outlined in this thread, I have done many clean installs in the past few weeks, followed by a Repair, which more often than not produces the Failed to load language dll error.
My faith in Avast's ability to produce a stable Windows 8.1/10 installation is dwindling rapidly. I believe (based on my experiences over the past couple of years with the Avast software) that with so many component option combinations available on install and with the forced/emergency updates, Avast have just not tested all possible scenarios on all platforms, hence the problems that have arisen that are outlined in this thread.