Most people write in Swedish here, but English, Danish and Norwegian often appear, sometimes mixed in the same thread. I searched but didn't find anything if there are any rules about language, would it be OK to write in French, Spanish, Mandarin if I felt like it?
Isn’t the site owner/administrator Norwegian? Believe he communicated in English sometime here.
Most native-born continental Scandinavians won’t be able to understand a lot of written French, Spanish and Chinese without a translator (even as the first two of those languages are very often offered as part of a mandatory foreign language elective at most schools in Sweden for kids in at least the sixth grade and higher). Most such Scandinavians under 60 years of age can typically understand written English without much problem, and English is part of the core curriculum in schools starting with class zero or first grade. Swedish three-year olds seem to be able to understand most spoken Norwegian, so I take it that understanding written Norwegian is probably not that hard to understand either once a person is literate in Swedish. Danish is the one of these three Scandinavian languages that seems to give Swedes a tougher time, but I find reading Danish pretty easy — although of course Swedish is even easier.
I was reluctant to post here in English and would be more reluctant to post in French or Spanish here even as I can write treatises in French public policy matters and had Spanish from kindergarten. Not because of any rule, but just because communication is communication when the language used to write works for the audience coming across the language.
And automated translation tools can be bizarrely inaccurate. For a view into that, just look at how Disney+ translations nowadays for captions/subtitles in Swedish are more bizarre now than translations used for Disney-produced content shown on Swedish TV 10-50 years ago. [Disney+ does the English>Swedish audio translation better than it does for the written subtitles/captions it adds in Swedish, and the difference comes down to the use level of automated translations.]