Is the word voltar the same in Brazilian and European Portuguese?

Yes

The word "voltar" is identical in meaning, spelling, and grammatical function in both Brazilian and Continental Portuguese. The differences are almost exclusively phonetic:

• The "r" sound: In many Brazilian dialects, the final "r" is often aspirated (sounding like an English "h") or very soft. In Portugal, the "r" is typically more pronounced and alveolar (a tap or a slight trill).
• Vowels: Brazilian Portuguese tends to have more open and clearly articulated vowels. In Continental Portuguese, unstressed vowels are often "closed" or reduced, sometimes becoming nearly silent.

Brazilian Portuguese Examples

1. "Eu vou voltar para casa agora." (I am going back home now.)
2. "A gente vai voltar a se falar logo." (We are going to talk again soon.)
3. "Ele voltou para o Brasil depois de anos." (He returned to Brazil after years.)
4. "Não quero voltar àquele assunto." (I don't want to go back to that subject.)
5. "Você vai voltar a estudar no ano que vem?" (Are you going to start studying again next year?)

Continental Portuguese Examples

1. "Eu vou voltar para casa agora." (I am going back home now.)
2. "Nós vamos voltar a falar em breve." (We will talk again soon.)
3. "Ele regressou ao Brasil após anos." (He returned to Brazil after years.)
4. "Não quero voltar a esse assunto." (I don't want to go back to this subject.)
5. "Vais voltar a estudar no próximo ano?" (Are you going to start studying again next year?)