I agree with you to some extent, but I must admit that I wasn't thinking about this from the point of view mentioned by "houtari" at the beginning. But more from the point of view of users looking at the map.

Yes, it is fair to admit that a small majority of the population speaks Swedish as their mother tongue, but it is an exaggeration to claim that the Swedish-speaking population is in a clear majority. Some places have done this elsewhere, such as Macau (“city state”) where place names on streets and virtually all other POIs are marked in both Chinese and Portuguese, although the language distribution is much clearer (Chinese is spoken by 80% of the popula). Still, both languages have official status, rather than being counted in terms of number of speakers; this could be compared to Finland, where both Finnish and Swedish have official status. In Finland as a whole, Swedish is spoken as a mother tongue by just about 5% of the population. But do they make a map for the local population, apparently yes, because given these statistics it is essential in a city of 6000 inhabitants to start getting upset that both official languages of the state are taken into account, at least according to you. However, the city of Kristiinankaupunki is bilingual in its official, administrative status. I understand the technical aspect, but in my editing the names in both languages were separately taken into account by the multilingual names tagging, so I would think the technical disadvantage in this case would be minor.