Question about doubles pairing in WTTC?

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so i haven't followed many doubles events so im a bit unsure...

In these doubles events i noticed ma long paired with timo boll and Fang Bo is paired with Solja petrissa from germany?

What is the reason behind why there is some cross nations pairing going on?

Don't get me wrong i find this quite interesting but i'm just wondering was it through some kind of draw (or which rules) that these pairings became to be?

And are there any other interesting pairings in this WTTC?