Count yes, swearing no. At least in my case. I often swear first in Chinese, and I didn’t learn my first Chinese word, which was some Cantonese swearing, until I was 15 working in a Chinese restaurant. Counting though and especially calculation, IMHO, definately is a sign of native speech.
English was the third language my husband learned, and it was through mandatory “English as a second language” classes at school (British-accented English, BTW). After living in the USA for many years, he speaks American-accented English most of the time, speaks his L1 somewhat frequently, and his L2 rarely. He says he dreams in English, but whenever he talks in his sleep, it’s in his L1.
I enjoy studying languages and will occasionally dream in the language I have been studying most recently. Not the whole dream, just phrases here and there. Never dreamt in Latin, though…wonder why.