From Wikipedia:
"There are two main theories regarding the origination of the uvular trill in European languages. According to one theory, the uvular trill originated in Standard
French around the seventeenth century, spreading to standard
varieties of
German,
Danish,
Portuguese, as well as in parts of
Dutch,
Norwegian, and
Swedish; it is also present in other areas of Europe, but it is not clear if such pronunciations are due to French influence.
[2] In most cases, varieties have shifted this to a
voiced uvular fricative [ʁ] or a
voiced uvular approximant [ʁ̞].
The other main theory posits that the uvular R
originated within Germanic languages through a process where the alveolar R was weakened and then replaced by an imitation of the alveolar R (vocalisation). As counterevidence against the "French origin" theory, it is stipulated that there are many signs that the uvular R existed in certain German dialects long before the 17th century."|
Could uvular trill have a substratal origin in Western Europe?
JS Lopes