Question I need help on translating that phrase from the caption of anime Batman Ninja.

Hi. Can someone please help me translating this?

この姿なら異国人も怪しまれない

I think it's something like "with that outfit, you won't be suspected (of something I don't know. Maybe of being foreigner)"

It makes sense to be suspected of being foreigner, but I don't see how the structure of the phrase can lead to that translation. The word 異国人 for me is more like the person that is being suspected by someone rather than of what the person is being suspected.

"With that/this outfit, you(or people in general) won't be suspected even if you are (or people in general is) a foreigner" makes sense?

Yes it makes sense. But doesn't the phrase need a でも after the 異国人 instead of just も? I am not too familiarized with those suffixes, but I see でも as the combination of the word で, meaning "to be", and も, meaning "even". So でも would mean "even if you are".

Do you know a proverb 夫婦喧嘩は犬も食わない? This も is "too/also" (or more accurately, "not~either"), and the nuance "even (if)" is given by the context (showing an extreme example), as same as your sentence.

Incidentally, indeed でも is originally made of the -te form of copula and も, but it's treated as a particle as a set. The meaning "even if you are ~" is from the context, not from で.