The description of the Speed Limit setting currently uses a lot of
complicated terms, like "emulated time" (known to many Dolphin
developers, but in my experience not known by even advanced emulator
users) and "maximum time scale" (I have never heard it before). The
meaning of "sustainable" is also unclear in context.

This commit rewords the description to be easier to understand.

i18n: Add comments and improve source strings

Add #if statements to only create and set analytics descriptions if
analytics are enabled in the build settings.