The dots above 'A (a)' , changes the hard vowel into a soft vowel = Ä (ä). It's an umlaut (german expression), often used for conjugations, like when the singular "man" becomes the plural "män", or as in human beings = Människor (but here also the singular is soft = en människa)

It's really a dilalect thing manisha is a Norrland thing and less commen in most of Sweden I would say mainihwa is more commen but your right both are said.

"en person" :)

Both are correct and both can be used to answer this now. :)

Well, mens in Swedish means period, as in the kind women have, which may be useful to know. About människa, it's a bit complex I think. We use person somewhat less than they do in English. In Russian, they talk a lot about 'the Russian human' in a way that is not natural in Swedish (when discussing how Russian people act and think). Like in your example, it's not grammatically wrong to say den tyska människan, but we rarely use that construction. It's more natural to say either something like den tyska killen/tjejen or tysken/tyskan if you're speaking about one specific person, or, if you're speaking about Germans in general, use the plural tyskar instead.

As an interjection, Människa! works pretty much the same as Mensch! in German. Suitable when you're upset.

Another interesting thing about människa, which I'm not sure we're teaching in the course, is that it is one of the extremely few words (maybe the only one left) which can be said to still have feminine gender, in the sense that if you ever need a pronoun for människan, it should be hon. Authentic example: Herr talman! Så länge människan har funnits här på jorden har hon förorenat. 'Mr President, for as long as mankind has been here on earth, he has been polluting.'

In some dialects, en människa is only used to refer to a female person.

tl;dr You cannot always refer to a person as en människa in Swedish, sometimes it will sound odd.

I don't fully understand what you mean with "cannot be used in Dutch always". It is somewhat context depended, but it's the preferred Dutch word to translate the English word "person". A kind person, I would definitely translate to "een goed mens" or "een aardig mens". "Een aardige persoon" does not sound as natural, though it's not wrong.

In general it's better to say "mens" then "persoon" in Dutch.

en människa = a human being (noun). But yes, we can say 'bara människa', meaning 'bara en människa' = I am just human/just a human being.

probably because "man" most generally means an adult male whereas "human" is distinctly any person of the human species. you wouldn't say "i know that man" if you saw a women you knew, would you? You'd most likely say something closer to, "I know that person" or "I know here"