hi, welcome new-abc and lpalmer
i started studying arabic just before i first visited a coptic church, so i found it easy to fit in, as i only needed to remember 3 or 4 arabic words and all the old ladies were suddenly introducing me to their friends!
it helps (i think) to go to a smaller church, if there are more than 100 people there, everyone will tend to assume you know someone there and they might not say 'hello'.
some copts are really shy, affected by years of being scared of outsiders (persecution in egypt and sudan is very bad) or just afraid that their english is bad, so they might not say 'hello'.
in other churches, i have visited, i have seen a mixture of reactions from being ignored to being welcomed like a long-lost cousin.
i think the important thing is to find a church where Christian life is explained in a relevant way, keeping close to the Bible and the church father's interpretations of this. it does have to be in the main language of your country for you to be able to check this out, or at least a good translation should be easily available. once the church has passed this test, see if people are kind (it means they understood the sermon). then if they still ignore you, stick with it, they are probably just shy. try going up to someone of your same gender and say 'hi, you have a nice church here' or something like that.
i hope you find friends, you shouldn't have to change your culture, but you may find a few greek or russian phrases come in handy.