A good question. It is possible that to translate "carries on" into Spanish may not have carried the same meaning as it does in English. In fact, it may even have conveyed something of a negative connotation. Just a guess on my part, though. "Eran Trece," translated into English, means "There Were Thirteen." This phrase is used in the film as a portion of dialogue spoken by one of the principal characters. It also has a good "ring" to it, and the layers of meaning of the number thirteen was surely an additional factor.
In the end, I think that the change in title was more or less a decision relating to ticket sales, mainly. It is very probable that Spanish speaking audiences were not as yet at all familiar with Charlie Chan as were their English speaking counterparts, especially Americans and Canadians who had had access to the Earl Derr Biggers stores as presented in 'The Saturday Evening Post' and in book form.
