In addition, when I click to "Open Calendar", "Execution of evolution -c calendar command failed: Command not found" notification appears. That button may not be shown if evolution is not installed.

(In reply to comment #1)
> That button may not be shown if evolution is not installed.

The button does not hardcode evolution, so if at all, it should be hidden only when evolution is not installed *and* configured as the preferred calendar application. Though I tend to only hide the button if the preference is unset (which we currently don't do iirc), so distributions that do not install any calendar application by default can use an appropriate override ...

Created attachment 212427 [details] [review]
Mirror Evolution calendar settings into our own schema

Right now, we are hard-depending on the presence of Evolution by
using its settings schemas. This is likely to be unpopular, and
also causes instability if someone happens not to have Evolution
installed, so install a schema that has the same data path as
the Evolution schema, but a different name and install that
for the keys we need.

To avoid a string-freeze break, we skip translating this new
schema.

Created attachment 212431 [details] [review]
Mirror Evolution calendar settings into our own schema

New version - the descriptions exactly match what is in
Evolution so as to pick up Evolution's translations properly

====
Right now, we are hard-depending on the presence of Evolution by
using its settings schemas. This is likely to be unpopular, and
also causes instability if someone happens not to have Evolution
installed, so install a schema that has the same data path as
the Evolution schema, but a different name and install that
for the keys we need.

To avoid a string-freeze break, we rely on the translations in
Evolution - if Evolution isn't installed, the key descriptions
will be untranslated in dconf-editor.

Review of attachment 212431 [details] [review]:

Looks "good" (as a workaround), so go ahead.

Pushed to master and gnome-3-4

Attachment 212431 [details] pushed as a64c843 - Mirror Evolution calendar settings into our own schema