Which letter of the Spanish alphabet, the only one of purely Germanic origin, was officially introduced by the Royal Spanish Academy in 1803, but its use was only definitively consolidated in the 20th century?

The letter 'w' (double vee or double u) is the only letter in the Spanish alphabet with a clearly Germanic origin. It appeared in words of Visigothic origin (such as 'Wifredo') but fell into disuse. It was officially reintroduced in the academic dictionary of 1803 to represent sounds from other languages ​​(such as English or German). Its use for foreign words ('whisky', 'watt') and some place names and proper names ('Washington', 'Wolfgang') became normalized in the 20th century. It is the twenty-sixth and last letter of the modern Spanish alphabet.