Learning languages can have many forms. Browsing through vocabulary at 4 secs per card on Anki is challenging to keep up for 2 hours in a row. On the other hand it's quite possible to do 2 hours of a Pimsleur tape in one setting.

Should learning of math be interrupted by short burts of learning a language or by complete rest?

I think it makes the most sense to switch mental and physical activity.

Could I learn math, a language and after that some biology?

Traditionally that's what's done in high school.