Even though Eira Kaho and Matsuri Dei are half-Brazilian and half-English respectively, they were born and raised in Japan, so they technically don't count as foreign characters. Nevertheless, it does show that the creators are willing to feature characters with roots outside Japan.
If Nakamura and Nozawa do decide to introduce foreign characters in the future, which countries should they come from: France, Germany, the United Kingdom, Ireland, Sweden, Lithuania, Finland, Estonia, Italy, Spain, Greece, Albania, Russia, Ukraine, Poland, Bulgaria, Hungary, Romania, Egypt, Armenia, Iran, Iraq, Turkey, Israel, Saudi Arabia, the United Arab Emirates, Kuwait, Bahrain, China, Taiwan, Hong Kong, South Korea, Vietnam, etc.?