SOLI DEO GLORIA
The word for "alone" in Latin here is soli, which is the dative form of the adjective solus. This creates a wonderful pun on the word for sun, which is sol in Latin, soli in the dative. So, in addition to meaning "To God Alone is the Glory," the Latin phrase also means "To God, the Sun, is the Glory."
For another sundial with this same Latin motto, see this beautiful image at the British Museum: 19th-century ivory diptych dial (see the motto on the lower dial). See also this diptych dial at the Royal Museums Greenwich.
Meanwhile, this Swiss sundial has a German inscription on a banner which I cannot read; if anybody can help me with this, that would be super! You can see a more detailed view here.