Their first language would be their country of birth. Maybe you mean their second language. Can Micky speak French? I know he was in Germany so should speak a bit of German.
Zlatans english will be very good from being a Swede since you are taught it at age ~4ish and then the majority of TV shows imported are American, and the internet really helps people with learning languages too. Then his time in Italy helps him, French/Italian/Spanish IIRC are all Latino languages so it helps enourmously.
There's a lot of crossover, just like with Scandinavian languages all being similar (for the most part) and having germanic origins means there's even similarities with english, german but of course there's false friends, you can't literally translate, there's different patterns of speech. sentence structure, tenses irregular verbs etc.
I think for Pogba his family being in Manchester means he's never really lost the accent, being French he would be speaking english quite a bit as an intermediate language eg if you have a german and a french person they would speak english as a middle-ground.
I'm surprised at Pogbas level of Spanish but again latino language helps but it's still a huge effort to learn a language it takes so much dedication and immersion I'm not sure where he's got it from. I can understand Pogba having Italian, English, French but Mkhitaryan even Rakitic no idea how they speak so many languages, I kind of expect Mkhitaryan to start speaking Elvish from LOTR in his post-match conference at this rate.