@maksanse – Using your specific example of the “Submit” string – As it currently stands, yes, bbPress is being overridden. I’m sure there are many other cases where that’s true as well. There is also no way to choose which translation file has priority either, and I’m not sure there’s a good solution for that.
The reason for it is due to Style Pack overriding the default bbPress templates (using Style Pack files). Therefore the bbPress translations (using bbPress files) won’t have any references to any Style Pack file translation strings (and vise-versa).
I’ve actually been working on a translation overhaul for about 3 weeks now. I hope to release it in the near future. The main goal is to make strings machine-translation-friendly, and to ship Style Pack with 10-20+ machine translations to cover many languages, and be able to add more quickly/easily as requested. Strings that both bbPress and Style Pack have in common should already “match” for each language. With that said, let me know any specific languages you would like to see included.
I will give this some thought, but I don’t know of a good way to accomplish your desired outcome of using bbPress translations instead of Style Pack translations, or to migrate bbPress translations over to Style Pack. Only thing to comes to mind is to write a custom script that will read the values specified within your custom bbPress translation files and then apply those values to any matching string within Style Pack files. Considering you’re the first person to bring this up, I’m not sure how many others would want/need that capability….but I’m willing to consider something like that if it makes sense. Always open to suggestions and ideas if you have any!