Why is Wales in the UK called Wales?

The word Wales derives from old German and means 'stranger' or 'foreign.' Derivatives of the word were applied by Anglo Saxons to the Celtic inhabitants of Britain.

Interestingly enough the French and Spanish names for Wales are very similar to the old Roman word for France - 'Gaul'. In Spanish is it 'Gales' and in French it is 'Pays de Galles'.