:MOS:RETAIN says, When an article has evolved sufficiently for it to be clear which variety of English it employs, the whole article should continue to conform to that variety, unless there are reasons for changing it based on strong national ties to the topic. I do not see how Catalan has any national ties to Commonwealth nations (nor does it have national ties to the United States or American English-speaking countries), so it cannot be argued that national ties are a reason to rewrite the English variety already present.