We often see depictions of natives who have descriptive names ('bright flower' or 'red fox', etc) and many old place names appear to be simple descriptions of the place (e.g. Milton = mill town).
In comparison, today we look up the meanings of names in baby books and names like London or the Thames don't mean anything in modern English.
When did this change? When and why did people begin using names that they didn't understand? Is this common in the test of the world?
(I apologize if this is more of a sociology question)
Most names mean something - but not always in English. London for example is from Londinium (a latin name) and may have come from it's founder Lud but we're not really sure. Thames from Middle English Temese, is derived from the Celtic name for the river, Tamesas recorded in Latin as Tamesis and yielding modern Welsh Tafwys "Thames". The name probably meant "dark"
There are many placenames in England with Celtic, Latin and norse origins. Sometimes they are anglicized over time to help with pronunciation or give it a more anglo spelling. For example, anything ending with "by" is of old norse origin meaning village/place (Grimsby, Derby, Whitby) anything with burgh/borough/bury is old english meaning fortified enclosure
Here's a cool (wikipedia) link on some parts of place names that give you an idea where they're from language-wise. https://en.wikipedia.org/wiki/List_of_generic_forms_in_place_names_in_the_United_Kingdom_and_Ireland
In terms of human names, they also usually mean something - again in another language. The most common English names all have meanings:
Robert: From the Germanic name Hrodebert meaning "bright fame", derived from the Germanic elements hrod "fame" and beraht "bright" (obviously changed over time)
Elizabeth: From Ελισαβετ (Elisabet), the Greek form of the Hebrew name אֱלִישֶׁבַע ('Elisheva') meaning "my God is an oath" or perhaps "my God is abundance" (this goes back to biblical, so maybe not an English name but pretty significant in English culture)
John: English form of Iohannes, the Latin form of the Greek name Ιωαννης (Ioannes), itself derived from the Hebrew name יוֹחָנָן (Yochanan) meaning "YAHWEH is gracious".
Thames, much like Avon, means River (though in which language I'm not sure). London comes from the Roman name for the settlement, Londinium, again I'm unsure on the etymology.
Place names such as Newton (New town) are Anglo-Saxon in nature.