I wonder if there is or was confusion/lack of understanding from US, of the English Language and English law?
Nah a person can literally not stand trial in the UK if it is shown that they are not capable of fully understanding the proceedings, eg a language barrier. They've got to know enough of what's going on to be able to understand the proceedings, this is why the trial and death sentence of say Timothy Evans in the 1950s was so controversial (and in any case he likely was innocent) because he had a low IQ and arguable didn't understand what was going on. There is a very good argument that has been made by several jurists and legal academics that the Bulger killers should not have been tried as adults because they were too young and ill-educated to understand what was going on, which I broadly think is true.
US seems to have married a polish woman to get EU citizenship and worked in various unskilled jobs, and run back to Pakistan when his daughter actually died of her abuse, which makes me wonder how much he really understood about living in the UK?
Oh nah don't give him the excuse, I will say this as a naturalised immigrant from a conservative culture myself - I am sure he understands British culture and values just fine, fine enough to work and avail himself of our public services etc. Don't give him the excuse. On physical chastisement of women and children, the Quran does allow light physical chastisement of one's wife but only once other non-violent attempts at 'correcting' her have failed. The Prophet spoke against hitting children. And torturing your own daughter to death is definitely not allowed by any religion afaik!