"They usually go to the west coast in summer."
Translation:De brukar åka till Västkusten på sommaren.
Proper names of places are capitalized in Swedish. This includes compunds, both those composed of two nouns and an adjective an a noun. E.g. Västkusten, Sydfrankrike, Östafrika, Sommarsverige. Compare these to västra kusten, södra Frankrike, östra Afrika, somriga Sverige. Sometimes both a compound and the adjective + noun are considered proper names, and both words are thus capitalized, as is the case of Mellanöstern and Mellersta Östern. However, proper nouns for residents of a place are not capitalized (stockholmsbo, göteborgare).
Oh, so maybe I should've submitted a report for a correct answer.
'They usually go to the West coast in summer,' and 'they usually go to the West coast during the summer' are essentially analogous in English. In fact, in this context, I believe 'during the summer' would be the more common expression, depending on what you intend to mean.
The English sentence in question here: 'they usually go to the West coast in summer,' is actually a bit nebulous because it's unclear what 'usually' wants to apply to. For example: 'they usually go to the West coast (but not always) | during the summer.' Vs, 'they go to the West coast, | usually during the summer (but not always).'
If you wanted to be more clear with this same construction, in English you might say: 'they usually go to the West coast during the summer.' Meaning that they usually go to the West coast, but always during or for the entire duration of the summer months. Or you could say, 'they usually go to the West coast for the summer.' This meaning exclusively that they go there for the entire summertime.
In either case, I would recommend changing the English sentence in this question to: 'they usually go to the West coast in the summer.' It sounds a little clearer and is more specific to its meaning. Especially considering that we see 'sommaren' which, to my knowledge, indicates 'the summer' anyway.