Claude Sonnet is the strongest fit for translating UI text while preserving the original voice, because it excels at following nuanced style instructions and maintaining tone consistency across short, context-sensitive strings. You can supply a style guide or sample copy and it will mirror the register, personality, and terminology across as many target languages as you need. ChatGPT is a solid alternative when you want a familiar interface with strong multilingual coverage, and Claude Opus edges ahead for the most demanding brand-voice fidelity where budget is less of a concern.