The Steam store page states that the game supports not just text language, but also voices for English and a few European languages (in particular, walker responses). The GOG page on the other hand states that only text localization is supported.

For those who bought the game here, can you confirm whether the game features voice acting on GOG too, and if the voice acting when changing the language also features the localized dubs as the Steam version does? Thank you.

You can change the Language of all Text and Voices in InGame Settings.
English, German, French, Italian, Spanish are available.

For German i can confirm, the original german voice samples are used.