You're assuming prompting an LLM to behave like X will automatically result in the LLM behaving like X for any X. Some things are out of the LLMs ability: I'm sure you'll get something if your prompt is "You are a 300-IQ nuclear physicist with a doctorate in material science. Describe the design of a cold-fusion reactor", but there is no guarantee the LLM has fidelity to your prompted persona, though it will try to give its very best impression.
I'm not assuming, I'm a native speaker and I describe actual experience with Claude. It's pretty good at roleplaying and major languages, with certain caveats. If you aren't a native speaker though, you'll have a hard time verifying that it gives you a good result, that's what I'm trying to say.
