The forum doesn't control what language file is used, that is the core. The error you are seeing here, however, it related to another culture related problem. The problem here is a decimal value (1.0 for example in US-en) is not shown this way in other cultures (ie. 1,0). This is identified as an issue via another thread here:
http://www.dnnforums.com/Resources/Fo.... I am leaving this one as the active thread (so I remember to fix it).