[Inkscape-translator] Translation of 'Apply' button

I have been searching for where the 'Apply' button is translated, the one in all the Filters and Extension subdialogs (where menuitem ends with '...'). There are usually two buttons; 'Close' and 'Apply' - the former is already translated to Icelandic, but the latter is shown in English.

There's no occurrence of 'Apply' in the PO/POT files, so it must come from the desktop environment (GNOME?) - the problem is from where? I've tried grepping the source code, but without clear results so far.

Does anyone know here it stems from?

Best regards, Sveinn í Felli