diff --git a/web/src/i18n/parity.test.ts b/web/src/i18n/parity.test.ts
new file mode 100644
index 0000000..fba3e25
--- /dev/null
+++ b/web/src/i18n/parity.test.ts
@@ -0,0 +1,46 @@
+import { expect, test } from "vitest";
+
+import en from "./en.json";
+import sv from "./sv.json";
+
+// Flatten a nested translation object into a map of dotted leaf keys → string
+// values, e.g. { objects: { columns: { number: "…" } } } → "objects.columns.number".
+function flatten(obj: Record<string, unknown>, prefix = ""): Map<string, unknown> {
+  const out = new Map<string, unknown>();
+
+  for (const [key, value] of Object.entries(obj)) {
+    const path = prefix ? `${prefix}.${key}` : key;
+
+    if (value !== null && typeof value === "object" && !Array.isArray(value)) {
+      for (const [childPath, childValue] of flatten(value as Record<string, unknown>, path)) {
+        out.set(childPath, childValue);
+      }
+    } else {
+      out.set(path, value);
+    }
+  }
+
+  return out;
+}
+
+const enFlat = flatten(en as Record<string, unknown>);
+const svFlat = flatten(sv as Record<string, unknown>);
+
+test("en and sv have identical translation key sets", () => {
+  const missingInSv = [...enFlat.keys()].filter((k) => !svFlat.has(k)).sort();
+  const missingInEn = [...svFlat.keys()].filter((k) => !enFlat.has(k)).sort();
+
+  expect(missingInSv, `keys present in en.json but missing from sv.json:\n${missingInSv.join("\n")}`).toEqual([]);
+  expect(missingInEn, `keys present in sv.json but missing from en.json:\n${missingInEn.join("\n")}`).toEqual([]);
+});
+
+test("every translation value is a non-empty string in both locales", () => {
+  for (const [name, flat] of [["en", enFlat], ["sv", svFlat]] as const) {
+    const bad = [...flat.entries()]
+      .filter(([, v]) => typeof v !== "string" || v.trim() === "")
+      .map(([k]) => k)
+      .sort();
+
+    expect(bad, `${name}.json has empty or non-string values at:\n${bad.join("\n")}`).toEqual([]);
+  }
+});