I’d like to translate OSM in Finnish and I’ve done that, but I don’t find some strings to translate. Some translations are not well translated as well, and fixing them is difficult because the searching from the strings is not possible. Is it or didn’t I just find this feature?
However, I haven’t found some Potlatch UI translations:
Where can I translate them?
It seems that you want to translate some strings in the online editor called Potlatch2 … you cannot translate “Openstreetmap” because that isthe whole project. YOu can define one component of OSM like a special web GUI or an editor 
Have a look at http://wiki.openstreetmap.org/wiki/Potlatch_2 to find out how to get in development about it.
I’ve tried to find the strings, but I haven’t find anything else apart these:
http://translatewiki.net/w/i.php?title=Special:Translate&group=out-osm-potlatch2-main
http://translatewiki.net/w/i.php?title=Special:Translate&group=out-osm-potlatch2-help
They are already translated by me, but the strings which I mentioned before, are not over there. Is it possible to translate them at all?
I doubt whether anyone reading this forum knows enough about Potlatch development to answer your question, otherwise they would probably have replied until now.
So I suggest you contact the Potlatch developers on the potlatch-dev Mailing list, they will likely be both able and willing to help you getting started.
Thank’s.
Edit: I asked about this on mailing list, and they answered, that translating is not possible yet.