feat(i18n): localize researchers, risk debators, research mgr, trader

output_language config now propagates to every user-facing agent.
Previously only the four analysts and portfolio manager respected
the setting, producing partial-localization reports with English
debate text interleaved with non-English analyst sections. Verified
live: 7 agents produce Chinese output when config is set to Chinese.

#575

tradingagents/agents/trader/trader.py

@@ -7,7 +7,10 @@ import functools
 from langchain_core.messages import AIMessage
 
 from tradingagents.agents.schemas import TraderProposal, render_trader_proposal
-from tradingagents.agents.utils.agent_utils import build_instrument_context
+from tradingagents.agents.utils.agent_utils import (
+    build_instrument_context,
+    get_language_instruction,
+)
 from tradingagents.agents.utils.structured import (
     bind_structured,
     invoke_structured_or_freetext,
@@ -29,6 +32,7 @@ def create_trader(llm):
                     "You are a trading agent analyzing market data to make investment decisions. "
                     "Based on your analysis, provide a specific recommendation to buy, sell, or hold. "
                     "Anchor your reasoning in the analysts' reports and the research plan."
+                    + get_language_instruction()
                 ),
             },
             {