Outside Portugal this anniversary is hardly noticed. The first document in the Portuguese language was signed on 27th June 1214 by King Afonso II - it was his testament.
Afonso became King of Portugal in 1212, succeeding his father King Sancho I. Born on 23rd April 1185 King Afonso did not pursue territory enlargement policies of his father and grandfather, the first King of Portugal of the Burgundy dynasty that established the country's independence, managed to ensure peace with Castile during his reign.
|The first official use of Portuguese: The Testament of King Afonso II.|
In the last decade of the thirteenth century, King Dinis The Farmer - (1279–1325) legalised Portuguese as the official language of the Kingdom of Portugal, following the example of his grandfather, King Alfonso X of Castile and Leon, who established Castilian as the official language of his kingdom during his reign, which started in 1252.
Although the Portuguese was only formalised this in Dom Dinis, as of 1255, the chancery of King Afonso III of Portugal, the Portuguese used it alongside the Latin in official documents.
A report (in Portuguese, of course) can be watched on RTP's website: Língua portuguesa é usada em documentos oficiais desde há oito séculos.
PS. Accidentally (or intentionally?) the two sons of the heir to the Portuguese throne, HRH Dom Duarte Pio, Duke of Bragança, bear the names of the two important champions of the Portuguese language: Dom Afonso de Santa Maria, Prince of Beira, Duke of Barcelo and Infante Dinis, Duke of Porto.