Currently I'm living in Germany and I only have Polish citizenship and thus a Polish passport. I read that you need to remain in Germany at least 8 years in order to apply for the German citizenship. So I'm going to apply for it in 2 years. I don't think having German and Polish citizenship would be a problem, right?
Just theoretically speaking, would a combination of Polish, German, American, Japanese, Singaporean, South Korean, Israeli and Swiss citizenships (and passports) be possible? Would any of these countries be problematic for a multiple citizenship?