Check: the language line under the voice in the picker. Budget voices are English only; Premium and Pro voices are multilingual, and pronunciation and accent vary by voice. The free preview always plays an English sample line, so to judge a voice in your language, synthesize three to five lines with it first. When they are ready, the Voices dock plays your lines one at a time, on their own and without the music, in the voice that speaks each one.
Fix: swap to a voice that fits your script’s language and taste. Only the swapped voice’s lines re-synthesize, and lines you already paid for in other voices stay yours.