Martial Experience
Martial Experience Level 5
Elf
Ancestry: Elf
You've crossed blades with a wide variety of foes wielding a wide variety of weapons, and you've learned the basics of fighting with nearly any of them. When wielding a weapon you aren't proficient with, treat your level as your proficiency bonus.
At 11th level, you become trained in all weapons.
Source: Advanced Player's Guide pg. 43