kcms/region_language: use alternating background for list items
These list items have content on both sides, separated by a potentially very large area of whitespace. This can make it hard to distinguish at-a-glance which items on the right side line up with which items on the left side.
The typical way to improve usability for such a thing is to use alternating background colors to separate list items in a way that isn't super visually heavy. Let's do it here.
BUG: 469102 FIXED-IN: 6.0
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