Menu: allow customizing line spacing in wrapped TextLabel text

Improve appearance of a couple long messages.

The language change warning message is now an unique string, removing a possible source of confusion for translators since the first part of the message ended with a coma.

Screenshots (Click to expand)

Here it is a comparison between old and new messages, plus an additional screenshot showing how the wrapped message is displayed if it used one more line (it may happen when the message is translated to another more verbose language).

current (line spacing 1 and 0)	new (line spacing 0.5)	new (longer text)