The text 'UV Vertex', though translation exists in the language file (po file), is not visible in the UI.
- Open new blender file.
- Select the default cube, Tab into Edit Mode, press 'U' to unwrap UV, select an option from the popup menu (ie. 'Unwrap')
- Drag the triangle top right to create a new window. Change the new Window to 'UV/Image Editor'
- While the mouse pointer is on the 'UV/Image Editor', press 'N' to open the sub-tool-bar on the right and notice the text on top 'UV Vertex'.
- File->User Preferences->System, select 'International Fonts' (ticked), and select a foreign language of choice other than English. Click the first two button (Interface, Tooltips) below.
- Go back to the 'UV/Image Editor' screen and you should now see that the 'UV Vertex' has NOT been changed.
- Check this against the PO file of the chosen language to see if this line has been translated or not. The entry should be (msgid "UV Vertex"). The block of code responsible for this exists in uvedit_buttons.c (at bottom of the source file).