Good point! I was wondering about it at first, but @oldbonsai mentions in Updates to Synonyms on Item Pages “no more than eight, no more than 64 characters per synonym, no blank ones, no duplicate ones”. I was also able to successfully upload
"meaning_synonyms": [ "Stube", "Gästezimmer", "Empfangszimmer", "Zimmer im japanischen Stil;mit Tatami ausgelegtes Zimmer;Zimmer…" ]
where the last meaning is 65 bytes and the entire thing is of course much longer.
Cheers,
André