I also consider that it is better to promote the English forum and populate it by encouraging people to use it instead of localized ones, rather to force anything.
...a good idea to stick to English as much as possible?
The English community is bigger, therefore more information is shared (not necessarily of a better quality), nonetheless probably has more professionals and filled with more issues to learn about.
I might be wrong, but in the IT world, most people will turn to international communities anyway, only a few will use localized forums, especially when it comes to such a niche product as opensource firewalls.
Everybody gets it, but in another beam of light: it's not about "English Only" as much as possible just because it's (should be) official, nor just because other languages are harder to understand and follow. While all these are true, I only say that important and generally applicable topics, like bug reports, feature requests, best practices advice, how-tos and so on and so forth would be preferable to be in English so that any one (or at least as many people as possible, now and in the future) to be able to understand them, easily find and spot them, easily see if somebody else had/ has the same issues or feature request as that first one has... you get the point.
And, of course, since human kind in its entirety is prone to solutions of minimum resistance (we are all lazy, so to say), let's imagine for a moment what happens if I would write Romanian here (my native language), and be fortunate enough to get answers in Romanian from Franco, Michael, Frank, Fabian, Comet, Elektroinside (he is able to answer in Romanian, though ) and most of, if not every single heavy poster around here, just because they are comfortable with Romanian.
Why would I ever write again in a non-native language?!?! I wouldn't!But to what degree I would be pushing the break pedal in helping the entire community, in attracting, maintaining and being useful for people speaking any other language than Romanian?...
Same goes for German speakers (maybe French too, soon if not already): I agree, the most spoken language in that community is probably German (and definitely German is spoken by far much more people than Romanian, not only here, but worldwide). But this is very likely to change here, considering that OPNsense/ Deciso aim to a worldwide impact.
BTW: You could translate the user interface to Romanian if you like.