First-party traits on the Kenku can be found on page 109 of Volo's Guide to Monsters and is copyright Wizards of the Coast.
On speaking and Kenkus
Notes from the Director: when playing a Kenku, describing the sounds you make may be more effective than actually performing them - which can come off as confusing or irritating. I rule that Kenku that have lived among other creatures can form simple sentences or thoughts in common, but Mimicry instead can communicate to, beguile, or trick others more easily. If you can literally mimic any sound, well, the possibilities are actually endless to the creative, but maybe favor description over actually trying to make the sound yourself.