Translation:He will have decided to swim.
Without a time word to set this in the future (eg I morgon kommer han att ha... ) this feels as though it could be happening currently or in the recent past. As in: "Where on earth did he get to?/Why is he not home yet?" ... "He will have decided to swim." Would this be expressed the same way? Should it be more "He is going to have decided..." which sounds messier but also has a more implicit future tense. Or would the tense change somehow? I am a bit tired right now so please correct me if I have gone astray in my thinking!
It's true that the English sentence is potentially ambiguous, will could express some sort of likelihood. We usually don't use this construction like that in Swedish. It's more idiomatic to use particles like nog or väl, or adverbs like säkert or antagligen instead. Han har väl bestämt sig för att simma 'I guess he has decided to swim'.
Oh Hej Arnauti! Tack för ditt svar... I did not get a notification that you had replied and now I am worried that I have missed out on answers to a number of things I asked in the past couple of days! I saw in a forum that there have been some issues since they updated the forums...?
That is a good explanation. I think I had figured that the Swedish phrase wasn't likely to take on the ambiguity of the English and your explanation clears it up well. I need to wrap my head around how to use "väl" in this way... it will come with time I hope!
The forums have been very buggy lately and I'm sure I've missed a lot of comments myself. I remember answering a few of your questions but I can't remember exactly which ones so I'm not sure I could help you find them either. The "Show activity" button on my profile page is one of the things that haven't been working properly for me lately :(
The good news is that Duo is actively working with the forums. https://www.duolingo.com/comment/24701177 The bad news is that new bugs seem to have cropped up in the process :(
I am sure I will come across your replies as I go back through everything for practice so thank-you for your responses even if I have not had the pleasure of reading them just yet! (I came across this one because I had not closed the tab and refreshed the page to check for a reply!!) Strangely I am getting notifications for responses on old forums (ie ones early in the course) just not the more recent stuff which is what I really want! I am sure they will sort it out though. Thanks again, I really appreciate all your help! :)