The pair first met on international duty when they both represented Sweden Under 21s.
They immediately hit it off and when the 28-year-old first joined Albion he moved into the same apartment block as Larsson who had just begun to settle at Birmingham City.
"When he was here, it felt like we were the only Scandinavians in Birmingham, so we stuck together," Olsson told the Sunday Mercury.
"When I first moved here, we lived in the same complex so he was just across the road to me. We hung out quite a lot. It was good to speak Swedish a little bit, even if you have other friends here.
"It's always good to hang out with someone who knows what's going on back home and how life is back there.
"We used to be able to talk about Swedish stuff together.
"We still keep in touch and with the national team we always hang out."