Take Eli Siegel’s trans of Basho’s most famous haiku:

Pond, there, still and old!
A frog has jumped from the shore.
The splash can be heard.

It adds a lot of stuff not in the original (“there”, “still”, “shore”, present perfect tense instead of simple present, etc.) just to squeeze out those syllables.

Harold Henderson provides the following literal word-by-word translation of the original:

Old-pond frog jump-in water-sound

That’s all the information in the original poem in eight English syllables although it’s not intended to be an idiomatic rendering into English. A good modern translation is Jane Reichhold’s

old pond
a frog jumps into
the sound of water

Which comes out to 12 syllables and is entirely faithful to the meaning of the original.

Also note that I never mentioned Elizabeth Bishop in this discussion; but I did cite one imagistic haiku-inspired poem by Amy Lowell.

I suggest consulting a readily available book like The Essential Haiku (The Ecco Press, 1994, ed. by Robert Hass) to get a feel for translations that approximate the duration of the originals. Some can be extremely terse:

I go,
you stay;
two autumns.
(Shiki; previously attributed to Buson)

That’s what the poem says; why pad it out? English and Japanese are very different languages.