Firstly you are talking about two of the best players we have ever produced. Two players who benefitted from coming through our system, speaking the language and above all in their pomp having the entire team play for them.
Nunez has had to move to a new Country, learn a new language and he is playing in a team that is setup to maximise the opportunities Salah gets. I mean Nunez had a 100% 12 from 12 record from the spot but still wasn't on penalties.
Maybe a more apt comparison would be Owen at Madrid and Newcastle especially the language barrier at Newcastle or Fowler at Leeds.
I'm sorry but I'm not sure the language barrier or the new league/teammates argument holds any weight. Football is football, here or wherever else. And if you're 8 yards out from goal unchallenged and the goalkeeper has given you 2/3rds of the goal to aim at, you don't blast it as hard as you can hoping for the best. New country, language barrier, absolutely anything else doesn't matter there. None of those things have stopped him being absolutely clueless in front of goal.
Owen at Madrid didn't' do anywhere near as poorly as people think. 16 goals in 45 appearances, 26 starts. Nearly half of his games were off the bench. And that was the version of Owen who had suffered injuries already and clearly wasn't as quick.
If I go on holiday tomorrow and end up playing for a local Spanish side at the weekend and I miss a one-v-one I'm not going to blame not knowing the team or the language as an excuse. I wouldn't be any more likely to score if I had been there 2 years and knew the lingo. If you can finish you can finish, I don't understand the endless excuses for him as to why he hasn't or can't.