I need a bit more help (knowing me probably a alot more help). I think I've done it correctly but I can't get Kodi to use the revised translation I've supplied.
I'm trying on my Windows PC to start with so I don't wreck my real Kodi installation.
I've edited AppData\Roaming\Kodi\addons\skin.experimental\language\resource.language.en_gb\strings.po
by copying a couple of items from C:\Program Files\Kodi\addons\resource.language.en_gb\resources\strings.po
#: xbmc/windows/GUIMediaWindow.cpp
#: xbmc/windows/GUIWindowFileManager.cpp
msgctxt "#14076"
msgid "Add to favourites"
msgstr ""
#: xbmc/windows/GUIMediaWindow.cpp
#: xbmc/windows/GUIWindowFileManager.cpp
msgctxt "#14077"
msgid "Remove from favourites"
msgstr ""
altered the msgstr to refer to Watching
but the context menu still refers to favourites