The 25-year-old Argentine has caught the eye since a summer move from Racing Club, and Mulumbu says that it helps that the pair are able to communicate with each other verbally.
"I can speak a little Spanish so I can help Claudio," Mulumbu told the club's official website. "I speak Spanish with him on the pitch and I used to speak Spanish with Gonzalo Jara Reyes on the pitch too.
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Mulumbu was full of praise for Yacob, who has three Argentina caps to his name, stating that he is a step ahead of anything he's seen at the Hawthorns to date.
"Most importantly the partnership works because he is a great player and has a good understanding of the game. He understands football and he has learnt very quickly how West Brom play - he has made a big impact. He has become the main player of West Brom.
"It's great for the team and I think our partnership is really good this year. Paul Scharner was good to play alongside but Claudio is one step in front of him because he has the capacity to stay in his position of holding midfield – he protects the defence – and he is the best partner I have had so far."