"Sweden is the country in Europe which has the most lakes."
Translation:Sverige är det land i Europa som har flest sjöar.
I'm also just learning Swedish so hopefully a native-speaker will chime in but according to Swedish Comprehensive Grammar:
de flesta + noun in indefinite plural form - is used to signify "most X in general" or "X as a whole", used usually only in the subject position. -- De flesta barn tycker om djur - most children like animals.
de flesta + noun in definite plural form - is the typical translation of the English phrase "most of the X". Can be used both as the main subject of the sentence or as an object. It sometimes also implies a comparison (whereas the first one does not) -- De flesta barnen sa att de tyckte om djur - most of the children said they liked animals -- Han fick de flesta rösterna - he got the most votes
flest + noun in indefinite plural form - used to refer to an object or a prepositional object of a clause -- as is the case in this exercise, "som har flest sjöar" is the clause in the sentence Hope this helps!
I wrote this sentence! I didn't just make it up, the source is here: https://sv.wikipedia.org/wiki/Europas_geografi, under Sjöar. I don't know whether they counted Russia, but I know that Russia in fact does not have a lot of lakes, instead rivers are very characteristic of their natural geography.
The Wikipedia article takes into account the lakes that are bigger than one hectare in size. If you include the smaller lakes as well, Finland has some 187 900 lakes, more than in any other country in Europe. This is what I was taught at school, so I suppose it depends on how you define the concept 'lake'.
In geography, the surface area of the water actually has nothing to do with whether you’re talking about a pond, a lake, or a sea. Most people are aware about the distinction between a lake and a sea, and that some lakes are inaccurately called seas and vice versa. But that there are lakes that people call ponds and ponds that people call lakes is less widespread knowledge. The difference is actually about depth, not area (which makes sense, since they’re, you know, water, not mirrors). Ponds are photic zones, meaning that sun light reaches the whole bottom and therefore the whole of their bottoms have vegetation. Lakes are aphotic zones, meaning that they are so deep that sunlight does not reach the bottom and they have parts with no plants. Using the surface area as criteria means that some ponds are included and that countless lakes are excluded in the figure. :)