That's what I meant by "talking about sentences". Any sentence can express different propositions when uttered by different people. Just have people speaking different languages. So clearly "means different things when said by different people" isn't half specific enough to have any dire metaethical implications.
We are speaking the same language. Yet we express different propositions when we say "I'm sitting at a table." This is not trivial; for example, various other sentences do not have this property. So the SEP quote, once interpreted correctly, is non-trivial, too, because it is quite clear that the writer did not intend your "speaking different languages" interpretation.
Also, you can divorce a technical notion of a sentence from that of a string of sounds; sentencehood might be a two-place predicate of a string and a language.
Another month has passed and here is a new rationality quotes thread. The usual rules are: