diff --git a/packages/opencode/src/util/locale.ts b/packages/opencode/src/util/locale.ts
index ec900b441679..0ff22cd320b2 100644
--- a/packages/opencode/src/util/locale.ts
+++ b/packages/opencode/src/util/locale.ts
@@ -1,16 +1,24 @@
+function systemLocale(): string | undefined {
+  const raw = process.env.LC_ALL || process.env.LC_TIME || process.env.LANG
+  if (!raw) return undefined
+  const base = raw.split(".")[0]
+  if (base === "C" || base === "POSIX") return undefined
+  return base.replace("_", "-")
+}
+
 export function titlecase(str: string) {
   return str.replace(/\b\w/g, (c) => c.toUpperCase())
 }
 
 export function time(input: number): string {
   const date = new Date(input)
-  return date.toLocaleTimeString(undefined, { timeStyle: "short" })
+  return date.toLocaleTimeString(systemLocale(), { timeStyle: "short" })
 }
 
 export function datetime(input: number): string {
   const date = new Date(input)
   const localTime = time(input)
-  const localDate = date.toLocaleDateString()
+  const localDate = date.toLocaleDateString(systemLocale())
   return `${localTime} · ${localDate}`
 }
 
diff --git a/packages/opencode/test/util/locale.test.ts b/packages/opencode/test/util/locale.test.ts
new file mode 100644
index 000000000000..49b560d24a5e
--- /dev/null
+++ b/packages/opencode/test/util/locale.test.ts
@@ -0,0 +1,30 @@
+import { describe, expect, test } from "bun:test"
+import { time } from "@/util/locale"
+
+describe("locale", () => {
+  const originalEnv = { ...process.env }
+
+  test("respects LC_TIME for 24-hour locale", () => {
+    process.env.LC_TIME = "da_DK.UTF-8"
+    const result = time(Date.now())
+    expect(result).not.toMatch(/AM|PM/i)
+  })
+
+  test("respects LC_TIME for 12-hour locale", () => {
+    process.env.LC_TIME = "en_US.UTF-8"
+    const result = time(Date.now())
+    expect(result).toMatch(/AM|PM/i)
+  })
+
+  test("does not crash when no locale env vars set", () => {
+    delete process.env.LC_ALL
+    delete process.env.LC_TIME
+    delete process.env.LANG
+    const result = time(Date.now())
+    expect(typeof result).toBe("string")
+    expect(result.length).toBeGreaterThan(0)
+
+    // Restore original env
+    Object.assign(process.env, originalEnv)
+  })
+})