This language prioritization subject is an ongoing discussion in the finnish OSM community that actually bumps up from time to time when some individuals seem to override the existing agreement in the wiki to obey this principle with as I see it quite light arguments like "we're in Finland let's use Finnish". Not taking to account the different language profiles of our municipalities. Some people usually from the municipal minority try to singlehandedly override this situation by creating their own local versions with eg. two names in the name field. But before going to action I think this should be properly discussed in the community which it never has. I'm also glad to restart an internal discussion in the community forum to sort this out properly if you see that would be required and/or alternatively try to organize the community to go these things through. But as I said firstly I really would like to know the causes of the complaints you mentioned.

This all said there is now one possbile argument I'll accept and that's for parts of the Raseborg municipality which was created when joining together several old municipalities. After this merge the new municipality Raseborg had Swedish as it's major language, and a result of this former Pohja (Pojo in Swedish) municipality (https://www.openstreetmap.org/relation/37373) now a part of Raseborg (Raasepori in Finnish) which earlier was primary finnish had to change their language prioritization. Of course they didn't change their road name signs overnight so there might still be some old road signs in this region where Finnish comes before Swedish. This municipality merge took place already in 2009, so they have had some time to fix things. Otherwise there is no similar history of language prioritization change.

Wiki ref ...
https://wiki.openstreetmap.org/wiki/Multilingual_names#Finland

Community discussion refs ...
https://community.openstreetmap.org/t/kaksikieliset-nimet-kartalla/4824
https://community.openstreetmap.org/t/mista-loytaa-nimistoa-paa-ja-vahemmistokielilla-muille-kuin-teille/127444
https://community.openstreetmap.org/t/kaksikielisten-paikkakuntien-nimikaytannoista/129300