diff --git a/@xen-orchestra/immutable-backups/src/directory.mts b/@xen-orchestra/immutable-backups/src/directory.mts
index a867c3a45b..09b5b87df4 100644
--- a/@xen-orchestra/immutable-backups/src/directory.mts
+++ b/@xen-orchestra/immutable-backups/src/directory.mts
@@ -8,17 +8,18 @@ export async function makeImmutable(dirPath: string): Promise<void> {
 // chattr processes all paths even when some are missing (it does not abort on the first
 // error), so every existing path is correctly lifted.
 //
-// Per-path "while trying to stat" messages (ENOENT) are silently ignored regardless of
-// locale — these are always expected for optional paths (.xva, .alias.vhd, …) that are
-// absent in delta backups.  chattr localises the error description but "while trying to
-// stat" is always emitted in English, so we match on that suffix only.
+// Per-path "while trying to stat" messages (ENOENT) are silently ignored — these are always
+// expected for optional paths (.xva, .alias.vhd, …) that are absent in delta backups.  chattr
+// translates that whole message, so it is run under `LC_ALL=C`: without it, every batch
+// containing an optional missing path fails on a localised system, which means no backup ever
+// gets locked there.
 //
 // Any other error (e.g. EAGAIN on NFS when the file is still open, permission denied) is
 // retried up to 3 times with a 1 s delay before being re-thrown.
 async function execChattrWithMissingFiles(args: string[]): Promise<void> {
   for (let attempt = 0; ; attempt++) {
     try {
-      await execa('chattr', args)
+      await execa('chattr', args, { env: { LC_ALL: 'C' } })
       return
     } catch (err) {
       const stderr = (err as ExecaError).stderr ?? ''
diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index 56e0abcbd7..88385421f3 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -16,6 +16,7 @@
 ### Bug fixes
 
 > Users must be able to say: "I had this issue, happy to know it's fixed"
+- [Immutable backups] Backups are protected again on file servers whose system language is not English: immutability was silently not applied at all on those (PR [#10182](https://github.com/vatesfr/xen-orchestra/pull/10182))
 
 ### Packages to release
 
@@ -33,6 +34,7 @@
 
 <!--packages-start-->
 
+- @xen-orchestra/immutable-backups patch
 - @xen-orchestra/web minor
 
 <!--packages-end-->