An Elf character is allowed to choose Giant as a Bonus Language, but the Core Rulebook grants an elf only “Celestial, Draconic, Gnoll, Gnome, Goblin, Orc, and Sylvan”.
This is caused by "Race Bonus Language ~ Giant" being present on line 104 of cr_abilities_race.lst on the latest master commit.
The descriptive text in the data for the Languages racial ability already correctly does not include Giant.