"Nie lubię mówić na konferencji."

Translation: I do not like to speak at conferences.

[Kusssya]

why is plural form here?

Nie lubię mówić na konferencjach -> I do not like to speak at conferences

[tobithegreat]

Because English. It could also be "I don't like to speak at a conference." But that sounds a bit wonky in English. English prefers to use the plural for this construction. Apparently Polish prefers the singular.

[zagadka314]

"I do not like to speak at the conference"

[Jellei]

Works. Although frankly, both sentences would make more sense with plural conferences.