I agree - to me, that is the main practical reason Europe is a special case well-suited to symbolic signs.
The US doesn't have nearly that issue, since we have tons of symbolic signs, and few languages, which share a ton of close cognates anyway. For instance, most Mexicans I've heard will use the verb "parquear" or "aparcar" to mean "to park" rather than "estacionar" - so as you might expect, they have zero trouble decoding a sign saying "NO PARKING 9AM - 6PM" which is one of the most complicated text-only signs you usually see.