Whenever an extra component is used (or the short version of it), the narrator will only say the first part:

/tellraw @p {"text":"Hello ","extra":[{"text":"there."}]}
/tellraw @p [{"text":"Hello "},{"text":"there."}]

Result: narrator only says "Hello ".

It does worth with the with component of translate though.

/tellraw @p {"translate":"Hello %s","with":[{"text":"there."}]}

Result: Narrator says "Hello there."

Expected result: the narrator says "Hello there." in all situations.

On top of that, the narrator also doesn't say selector results.

/tellraw @p {"translate":"Hello %s","with":[{"selector":"@p"}]}

Result: narrator says "Hello ".
Expected result: narrator says "Hello <PLAYER>".