Hi, I had to use a user-defined locale with boost::format and had to add the following lines: version: 1.33.0 file: format/feed_args.hpp function: put 133 basic_oaltstringstream<Ch, Tr, Alloc> oss( &buf); 134 specs.fmtstate_.apply_on(oss, loc_p); 133 basic_oaltstringstream<Ch, Tr, Alloc> oss( &buf); + if (loc_p) + { + oss.imbue (*loc_p); + } 134 specs.fmtstate_.apply_on(oss, loc_p); I'm not sure if this is the right fix nor I am sure, if there are other uses of basic_oaltstringstream, which need to be fixed. At least for me it works after that change. Best regards Olaf Krzikalla