Try to open a file when in a different language and the text 'Open Blender File' on the button is STILL in English. This text exists in the PO file but the code doesn't appear to use the correct function to allow translations coming through.
The code is found in wm_files.c
void WM_OT_open_mainfile(wmOperatorType *ot)
ot->name = "Open Blender File";
ot->idname = "WM_OT_open_mainfile";
ot->description = "Open a Blender file";
Here is the image: