Only RM employees can speak to what RM's plans might be for support for Danish or other languages in the future. In the meantime, here is my understanding of RM's existing support for languages as it might apply to Danish.
RM supports the UTF-8 character set. That means that you can enter person's names, place names, etc. using Danish letters. Such names will appear properly in reports.
The only collating sequence supported by RM is a proprietary collating sequence that is not very suitable for Danish. It seems to me that language specific collation is a requirement for proper language support.
RM supports sentence templates. All the default sentence templates are in English, but you can change the defaults to Danish. The task can seem daunting, but I suspect that most RM users only use 15 to 20 different sentence templates at most. So, for example, you can change "born" to "født" in the sentence template for the birth fact, and the change will be made for all the birth facts in your entire database - and similarly for the death fact, the marriage fact, the burial fact, etc. It's not just individual words you can change, it's entire sentences. My Danish is not good enough to construct an entire birth sentence in Danish. (Jeg snakke liten Norsk, så kan jeg snagge liten Dansk, men bare liten.)
It does seem to me, however, that there are a couple of problems with RM's sentence template support as regards languages other than English. One problem is that there can only be one set of sentence templates. If you change your templates to Danish and then for some reason want to print a report in English, you will have to change all your templates back to English and your Danish templates will be gone. RM does not support the idea of a library of templates, where you have a set of English templates, a set of Danish templates, etc.
But of more importance, there are sentences that occur in reports that are not under the control of RM's sentence templates. I can't speak to every possible report, but for the register and modified register reports, there are two problems. One problem is that for the sentence about the person's spouse, part of the sentence is not under the control of a sentence template. The other problem is that the register and modified reports include a summary of the children for each family before carrying the children forward to the next generation. The summary of the children is under control of sentence templates if the children are not carried forward to the next generation, and the summary of the children is not under control of sentence templates if the children are carried forward to the next generation. This is a very serious problem in RM for any language other than English.
The RM user interface, Help files, etc. are fully in English. In my experience, this is common with lots of software, even if the software otherwise has good language support. I would expect the RM user interface to remain fully in English even if its support for collation and reports improves for other languages.