The translation from the raws puts the title as "Stranger, Dive Into the Dungeon." - with the three-kanji character "異邦人" translated as "kotokunibito" - "Stranger".
If you separate the kanji for "person" (人) from the end of kotokunibito, it becomes "異邦 人" - "Ihou hito" - "foreign country person" (we would say "foreigner"). Given the isekai nature of the plot, I would personally go with "Stranger, Dive Into the Dungeon" for the English title given that "foreigner" implies he came from some other country in THAT world, rather than being summoned from a different world.
But translation is an art more than a science, and I'm no artist when it comes to the Japanese language. This title is just my suggestion, not a demand.