"His wife is coming home tomorrow morning."
Translation:Hans fru kommer hem i morgon bitti.
This is the first time I see the word "bitti" :$ Can someone explain me when it is used exactly?
It is used only in the expression i morgon bitti and it means tomorrow morning.
No, this means she is coming home, it’s the literal use of kommer. Not the use of kommer as in forming the future tense, so you cannot ’replace’ it with ska.
I tried Hans fru kommer att komma hem i morgon bitti, but this was marked wrong. How can I tell when kommer att is okay and when it isn't?
is coming home is present tense in English, even though it can sometimes have a futural meaning like here. However, in Swedish it is much more common to use the present tense with a futural meaning than it is in English. Therefore it doesn't make much sense to translate an English sentence with present-for-future into a Swedish sentence in the future tense.
The other way around though is often a good idea.
So Hans fru kommer att komma hem should be His wife will come home or …is going to come home in English.
There are two kinds of kommer, one is the future construction kommer att which is a lot like 'is going to' in English. Here, you can skip att in spoken or informal language.
The kommer in this sentence really means comes. This is not a modal or auxiliary verb. You can't have an att after this one.
I put: I morgon bitti hans fru kommer hem. Should this be considered acceptable or no? It does not seem to change the meaning of the sentence...
Your sentence is ungrammatical because the verb absolutely has to go in second place in main clauses. You can rearrange other stuff, but kommer must be in second place.
I morgon bitti kommer hans fru hem.
Hans fru kommer hem i morgon bitti.
?Hem kommer hans fru i morgon bitti (this sentence is grammatically correct but not an accepted answer here because it's so special that you'd need to add some specific context for it to work).
One 'place' in this sense is a sentence constituent, it can be much longer than one word but it's something that could in principle be replaced with one word. Longer post about word order here: https://www.duolingo.com/comment/8970470
Tack så mycket, Arnauti. Ett lingot för dig... Jag glömde igen om de fördömda verbet placering.