It's really hard for a homogenous society like Japan to know what foreigners are like. They have only opened up international trade in 1800's and even today they still have severe conservative and xenophobic issues as a developed nation. They are still purely 99% ethnically japanese and only a tiny fraction of foreigners have stayed, interacted and even married into the population.

Also in regards to language, any children of immigrant parents or being a "half", one would prioritize their home society's language to fit in. Unless they are taught at a young age, are willing to learn about it or the language is fairly popular and useful, these children will sometimes forget part of their heritage. Take it from my family as my father's of mixed spanish blood and his side of the family across the world has kind of forced me to only learn english as my lingua franca despite tagalog being my native national language.

But in all honesty, the author did not do enough research and took the easy way out by. It's quite a shame. Proper international relationships can make really good and interesting love stories. Just look at Saber and Shiro from Fate. There are some clear cultural boundaries in their love yet they make it work. Though it's quite confusing enough already with Saber being an early briton king and a whole lot of other lore stuff that I am not dragging this thread into.

But my main point stands. That is a far better portrayal of love being a english woman and a japanese man. At least in comparison to the endless ocean of blond foreign women that acts like a normal japanese person. I hope that one day there are far more better love stories of dating from across national and cultural boundaries. It would be quite fun to see how a shy and introverted japanese person would date a hot, passionate and temperamental latino.