right, so shouldn't it's plural form be Dutchman instead of Dutch the singular form?
It's beta; there are guidelines. Capitalization in Swahili is similar to English.
For this sentence, what's the difference between saying "They are Dutch", and "They are Dutchman"?
"They are Dutch." refers to their nationality. "They are Dutchmen." would be grammatically correct (man is singular), but makes no sense to me.