Comment # 3 on bug 1106477 from Ladislav Slez�k

Interestingly after switching to "de_AT" the "Fallback language en_US will be
used" error is displayed but the primary language value is changed to "de_AT"
and the "Adapt Time Zone to Europe / Germany" check box is changed to "Adapt
Time Zone to Europe / Austria".

After saving the values the "en_US" is actually set, but if you select the time
zone switch then it is changed to "Europe / Austria".

The behavior is confusing and and the user has no clue which settings were
really activated, you have to start the modules again and check.