I didn't see any mistranslation nor saw anyone give a translation. The comfort part was Joseph putting the blame on himself, implying Keira was doing the same due to lack evidence during the investigation. Joseph seem to direct it to himself instead. It wasn't really comforting per-say (I said it bc I saw someone else say it so I went along with it), he seem to genuinely blame himself but also because it's possible he didn't want Keira feel like she failed. So he apologized instead.

There's a panel zoom on his eye looking at her as Keira talk about the investigation and no evidence, the next panel was her gloom expression. So he probably took notice of it and the next dialouge was Keira saying how there no traces of poison then right after that Jospeh apologizes, so that's how you kinda connect the feeling and atmosphere of the scene. Putting the blame on himself instead of Keira.