Yes. Spencer comes programmed to understand and respond in English, and you can reprogram it to use another language.
One of our customers did exactly that in Slovenian. His source code is on GitHub, and he wrote up a step-by-step guide with additional explanations on our community forum.
Spencer is no longer in production, so this is a community route rather than one we maintain, and how well it works will depend on the language you choose. If you get stuck part-way, message us here, or email [email protected], and we will help where we can.