Translate the system prompt and the individual / group persona prompt
builders in backend/app/services/oasis_profile_generator.py from
Chinese to English. The base prompt language was biasing persona
prose (bio, persona, profession, interested_topics) toward Chinese
even under Accept-Language: en, despite the existing
get_language_instruction() postfix mechanism. Translating the base
prompts removes that bias.
All locale-steering call sites are preserved verbatim (the inline
{get_language_instruction()} in each builder, the system-prompt
assembly), so non-English locales continue to receive Chinese output
of equivalent quality. Locale-independent constraints stay English
inside the prompt: gender stays the literal "male"/"female" enum
for individuals and "other" for groups; age stays an integer (30
for institutional accounts). The two attrs_str / context_str fallback
defaults ("无", "无额外上下文") are translated to "None" /
"No additional context" so they compose with the English body.
The country-language hint country: 国家（使用中文，如"中国"） is
dropped during translation; locale now decides the country language
via the postfix.
Out of scope (untouched): logger calls (issue #6, already merged),
docstrings and comments (issue #7), the rule-based fallback
_generate_profile_rule_based, and the resilience helpers
_fix_truncated_json / _try_fix_json. No public API change, no new
dependencies, no edits outside the target file.
Closes#3
3793c960e8