blocking non english clients would help because it might discourage the huge part of the chinese "community" from playing here in the first place. gettting rid of a huge portion of undesirable players. and only the ones with good enough english skills would remain. that would not solve all problems the server has but it would help alot.
also playing with a foreign client is just silly. you can't use many addons that rely on the english language, when you link items ppl need to click them first to find out what you are talking about.
with the foreign clients the chat usually looks like this:
Xiaopengwang: 5G [] YYYMMMM [] 2G [] 3G MMYY
Lebagutte: [Le Baguettefury, Baguette baguette de le Baguette]
Bratwurst: WTB [Rotzkotz der rostigen Rotzkotzigkeit]
Xiaowangzhung yells: BL BL bu br YYY
Pengwangxiao yells:
Xiaolongwang yells: 5G
etc