In languages in which all nouns are gendered,how is it decided what gender new words are?

in swedish, we have two gender, one neuter and one common. the common gender was once two gender, feminine and masculine(as it is now in german).

all the words with common gender(en-words) are tings that are living or that has to do with the human body. some examples are:

en näsa = a nose

en panna = a forehead

en hand = a hand

en for = a foot

you can also see some traces of the old masculine and feminine genders in the common genders. for instant, words that ends with an a used to be feminine words. and sometimes it's quite logical that they should be feminine, for example the word "blomma", which means flower. that just seems like a feminine word to me.

the words with neuter gender(ett-words) are things that are not living or has to do with the human body(of course there are exceptions of this). some example of ett-words are:

ett företag = a corporation

ett samtal = a conversation

ett rum = a room

ett tak = a roof

ett konstverk = a piece of art

all genders in european languages derive from the proto-indo-european language(that all indo-european languages derive from), which had two genders, animate and inanimate. so basically, the first gender system came from the division of things that are living, and things that are not. later on, the inanimate gender broke into two, feminine and masculine. many indo-european languages has all these three left, like german, most slavic languages and latin and greek. some has lost the neuter gender, as are the case of the romance languages, and some has melted feminine and masculine into one, like swedish and some other germanic languages. english and afrikaans has no genders at all left. anyways, sorry if my english was bad, and hope this answered your question! :)

The people decide. Sometimes both genders can be used. I hear spanish speakers say both " el walrmart" and " la walmart". Hip hop would be " el hip hop" and computer there is already a word for " la computadora".

People decide.

In greece heavy metal is called both η μέταλ (feminine) and το μέταλ (neuter)

But usually there is a set of rules eg we use feminine form for names of countries