The language barely phased Senku. He didn't treat people any differently, really, mostly recognizing them for who they were and how they could help with science. Thinking maybe that John was a student or something similar, he waved him in and handed a vial out.
"Oh, good. Perfect timing. Do come in and if you'd like to make yourself useful, I could use another hand. Trying something new, you know, so, it would be beneficial to have another hand in the room. Don't forget to put on a pair of goggles. Last thing I'd want is for someone coming at me because they got chemicals in their eyes." He nodded to the row of safety goggles lined up by the door. Like this was a perfectly normal experience.
Senku did glance at the stranger, though, curious as he met his gaze, but at the moment, he was just someone useful.