No translation of "palanque" to English is available. "podium" is the most usual translation of "palanque" and should be added. "palanque" must also be added as a possible translation of "podium" to Portuguese in the English-Portuguese dictionary.
According to the Dicio dictionary , this platform could be used in other contexts besides speeches, such as parties, but I have never seen it used in such contexts in southeast Brazil. In parties, we'd usually use "palco" (= stage ).
I conclude that a palanque is a 'stand, covered platform, stage'. There are other terms in English (dais, tribune, rostrum, bleacher) but each of these is qualitatively different in some way or other.
It appears that palanque is a sort of augmentative derived backwards from palanquim 'covered litter for one passenger', a loanword of Goan origin. Obviously the covering or roof is the key element linking the two terms, and it is for this reason that stand seems to me to be the nearest translation.
[Edit: If the structure is intended for speakers rather than important onlookers, then it may be referred to as a stage or platform rather than a stand.]