Level Up: Advanced 5th Edition has it where weapon proficiencies are based off of the Culture you grew up in. So, you could be a human who grew up in a Mountain Dwarf Culture and learned their weapon proficiencies.Which reminds me -- weapon proficiencies shouldn't be a right of birth, but instead awarded based on culture/upbringing.
Ah. My apologies. I did not notice the date, only the recent reply. Given the current lack-of-consensus regarding whether it is good or bad for stats to come from Background instead of Species, I had thought it was dramatically more recent. Six years is a long time.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.