JD, trek's explanation for why different species understand each other was always the UT - never a 'federation standard' - as I said, THIS was the scenarists' intent.
No, not really. At least, it depends on which "scenarists" you're referring to. The concept of the UT was first introduced in "Metamorphosis" as a special device that was used for specific purposes, in this case trying to communicate with an energy being that didn't have the capacity for normal speech. It was depicted at a flashlight-sized cylinder, so it clearly wasn't something that everyone had on their person 24/7, since we'd never seen one in use before.
True, later Trek has retconned the UT into a more ubiquitous device, in order to rationalize Trek's prior and ongoing use of the "every alien speaks English" conceit of sci-fi television. But that just makes it
one means for interspecies communication, specifically a means of facilitating communication between species that have never encountered each other before. It is illogical to assume that that precludes every other possible method of communication, such as actually
learning another language.
Case in point: Picard and Riker were both shown to gain a fair proficiency in Klingon, actually learning the language itself. Clearly people in the 24th century, particularly in Starfleet, are not lazy idiots who let machines do all their thinking for them, but intelligent, inquisitive people willing and eager to learn new things even if they don't strictly "need" to.
