diff --git a/AGENTS.md b/AGENTS.md
index 06e391a..640e106 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -23,6 +23,36 @@
   Resolve locally determinable engineering problems from the existing code and
   canonical documentation.
 
+## Repository language policy
+
+The canonical language of the Lardon3D repository is English.
+
+This applies to:
+
+- README.md;
+- AGENTS.md;
+- all current and future files under docs/**;
+- prompt.md and all files under prompt/**;
+- source comments under include/lardon3d/** and src/**;
+- developer-facing technical documentation, diagnostics and engineering contracts where applicable.
+
+The repository must not intentionally mix French and English technical prose.
+Existing French documentation and source comments are to be converted to English during the planned documentation and source-comment remediation passes, without changing scientific meaning, FROZEN facts, historical evidence, numeric values, identities, lifecycle truth or contract authority.
+
+Historical documents may be translated, but translation must not modernize or reinterpret the historical state they record.
+
+User-interface language is a separate product concern. Existing TUI labels may remain in their current language until an explicit localization/product decision is made. Repository language policy does not require the UI to be English-only.
+
+Canonical markers:
+
+DOCUMENTATION_LANGUAGE=ENGLISH
+
+SOURCE_COMMENT_LANGUAGE=ENGLISH
+
+AGENT_CONTRACT_LANGUAGE=ENGLISH
+
+USER_INTERFACE_LANGUAGE=INDEPENDENT
+
 ## 2. FROZEN integrity
 
 The following current project foundation is protected and may change only
diff --git a/docs/audits/documentation_inventory.md b/docs/audits/documentation_inventory.md
index cc45d39..e0868b0 100644
--- a/docs/audits/documentation_inventory.md
+++ b/docs/audits/documentation_inventory.md
@@ -414,6 +414,23 @@ docs/architecture/task_kind_registry.md states sixteen kinds but points to a Res
 
 The heading and cross-link must be synchronized without altering historical fourteen-kind audit evidence.
 
+# Repository language decision
+
+Human authority has selected English as the canonical repository language.
+
+The final repository target is:
+
+- DOCUMENTATION_LANGUAGE=ENGLISH
+- SOURCE_COMMENT_LANGUAGE=ENGLISH
+- AGENT_CONTRACT_LANGUAGE=ENGLISH
+- USER_INTERFACE_LANGUAGE=INDEPENDENT
+
+All technical documentation, agent contracts, prompt files and production source comments are to converge on English during the remediation passes.
+
+Translation must preserve scientific meaning, historical truth, FROZEN contracts, identities, numeric values, lifecycle state and evidence. A historical document may be translated but must not be silently modernized.
+
+The TUI language is a separate product/localization decision and is not changed by this documentation-language decision.
+
 # Product documentation intentionally deferred
 
 This documentation cleanup must not invent final contracts for: