In Spanish translation, the 'C' key is used as shortcut for two different items ("_Cerrar" button and "_Comprobación ortográfica" item). I suggest using 'o' instead for the orthographic check.
Fixed, moved to "o". Now just wait for the automatic script to pull the new strings.
Fixed in: https://git.xfce.org/apps/xfce4-dict/commit/?id=cd5729178a0034c6f00ae01e50ed3a8066f52612 Thanks Pablo, it'll be available in the next release (0.8.1).