Talk nineteen to the dozen is a popular expression of the Portuguese language and means talking too much, chattering.
The equivalent of the expression "to speak for the cotevelos" in English would be "talk nineteen to the dozen" (the literal translation being: say nineteen to half a dozen) or "talk a blue streak" (speak like lightning). However, these two expressions not only mean talking a lot, but also talking quickly.
expression source
The expression "speaking through the elbows" is a metaphor, since in reality, no one speaks physically through the elbows.
As it means "talking too much", this expression comes from people who have a habit of talking too much. These people, because they have this characteristic, can see the lack of interest in their interlocutor, since a person's attention span is limited, especially when the conversation is not interesting. So, in this case, the person who talks too much touches the other person's elbow to get their attention. It is for this reason that a person is said to "speak for the elbows". The first record of this expression is by the Latin writer
Quintus Horatius Flaccus (65-8 yr. C.), in one of his satires.Also regarding the expression "talking through the elbows", Brazilian folklorist Luís de Câmara Cascudo mentioned the custom of wives in the sertão northeastern man of touching his husbands at night with his elbow, while they were in bed, looking for reconciliation after a disagreement during the morning.