Is it forbidden in Islam when headscarf-carrying Muslim women get good mood through conversations before marriage with foreign men (eg by flirting)?
Is there any evidence, or notes from the Koran and or the Hadith ?
No, to have a good mood is not forbidden, but the Muslim woman should not flirt with men or otherwise do something because it is banned in Islam when making intimate stuff with the other gender or an unauthorized / non-Islamic relationship leads. One should, if you seriously say with the relationship, best marry, because that's Halal.
No, good mood is of course not Haram, on the contrary.