Green’s Dictionary of Slang

1. to speak.

1859		Hotten Dict. of Modern Sl. etc. 114: voker to talk; ‘can you voker Romany!’ can you speak the canting language.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 218/2: Can you ‘voker romeny’ (can you speak cant)?
1873		Sl. Dict.

2. to understand.

1861		Melbourne Punch ‘City Police Court’ 3 Oct. 234/1: The Mayor. – Oh, I can voker Romany as well as you; so shut your gob, and don’t be kicksy. What’s become of your mollisher?
1977		D. Powis Signs of Crime 206: Voker? Do you understand?