The phrase "speak american" was common from just before World War I to the mid 1930s. There was persistent antagonism between Americans and Brits, especially the English. In the late 19th Century they almost went to war over the Alabama affair. Understand that they were not allies in World War One, They were best described as Associated Powers, and there was significant ill feeling between the two nations. If Germany hadn't been stupid and had produced propaganda as vivid and well done as the English, American would have let the UK twist in the wind. Antagonism lead to an assertion of American identity down to language. Americans used the phrase "speak American" to separate themselves from English culture. Friction was so great that by 1935 it looked as if the US and the UK would go to war. Both sides made serious war plans. In the UK the phrase "speak American" was used as a sneering insult.
I'm sure our hispanic poster did not know this. But when one wears one's ethnic identity as if it were a star of David, then one will take offense without pursuing the facts.
There are many things over which to fault the Watchtower Society. This isn't one of them.