I'm still a bit confused. Why doesn't 'lange' have an 'n' at the end (like 'langen')? Isn't this meant to happen for plural nouns?
Would Die Frau hat langes Haar work as well? It's not ein Haar, so doesn't mean a single hair. Or, for example, Meine Haare sind schwarz VS Mein Haar ist schwarz, is there any preference for using one of these expressions? Thank you.
Both are correct and currently in use. The plural version is more colloquial.
I don't think so. You can't just switch it to singular, and leaving off the indefinite article is irrelevant. Consider the equivalent, changing "she has black dogs" to "she has black dog". See? Nonsense.
You can only trick yourself into believing it might work because "hair" in English is both singular and a bulk noun, so it still sounds kind of right to say hat Haar. But it just doesn't work that way in German.
Yes, it does work like that in German:
I thought this is a strong inflection as there is no article. So why is it "lange" and not "langes" to match a neuter noun like the rule says!!!!!
I guess your confusion is because the German sentence uses the plural, but the English seems to use singular? Well, think about it - the English sentence does not mean she has a singular long hair. English uses a mass noun here to refer to an amount of something that can't be counted (like "sand" or "water"). German just usually uses the plural in this specific situation.
Technically, both are correct, but because of that fact, the plural form is more commonly used in German.
I have just noticed that hair in German has a plural form. Are there nouns that are uncountable in German? If so, how much do they differ from that of English?