Custom Field Widget: Dependent Selectors

Only at Contact level, two Selector Custom Fields can be connected so that the values of one of them depend on the selection made on the other one. In the example below, the first Custom Field is for Language (like English, Swedish, etc), and the second Custom Field is for Dialect (like Welsh or Cork for English).
|The values for Dialect are to be configured like this:
<English>: Standard
<English>: Welsh
<English>: Cork
<Swedish>: Standard
<Swedish>: Gheg
Etc. 

In the Contact window, when selecting English under Language, Dialect lists: Standard, Welsh, Cork.
And when selecting Swedish under Language, Dialect lists the Swedish dialects.