[Bug]: Backup failure toast crashes on formatPlural IllegalArgumentException

[piotr-iohk]

What happened?

On production 2.3.1 (build 184), Play Vitals reports 2 crash events (1 user) with:

java.lang.IllegalArgumentException
  at android.icu.text.MessagePattern.parsePluralOrSelectStyle (MessagePattern.java:1157)
  at android.icu.text.MessageFormat.applyPattern (MessageFormat.java:449)
  at to.bitkit.ext.StringKt.formatPlural (String.kt:35)
  at to.bitkit.repositories.BackupRepo$showBackupFailureNotification$1.invokeSuspend (BackupRepo.kt:440)

When periodic backup check detects failed backups, BackupRepo.showBackupFailureNotification() formats settings__backup__failed_message via ICU MessageFormat. Parsing the pattern throws before the error toast can be shown.

Expected behavior

Failed backup notification should display localized retry message (e.g. "Retrying in 1 minute") without crashing.

Steps to Reproduce

1. Use Bitkit with locale set to a language with a malformed settings__backup__failed_message translation (suspected: Italian, Czech).
2. Trigger a VSS backup failure so showBackupFailureNotification() runs (failed backup detected on periodic check).
3. App crashes with IllegalArgumentException in formatPlural.

Suspected malformed translations in repo:

• values-it/strings.xml: {interval, plural, one {# minute} o {# minutes}} — uses o instead of ICU keyword other
• values-cs/strings.xml: {interval, plural, one {# minute} dalších {# minutes}} — missing other branch keyword

English pattern (valid): {interval, plural, one {# minute} other {# minutes}}

Logs / Screenshots / Recordings

• Play Vitals screenshot (2026-07-13 weekly report)
• Stack trace above

Bitkit Version

2.3.1 (build 184) — production mainnet

Device / OS

Motorola ThinkPhone 25 by motorola, Android 16 (SDK 36). Likely non-English locale given suspected malformed ICU plural translations.

Reproducibility

Rarely (once or twice) — 1 user / 2 events on 2.3.1 since Jun 29 rollout. May be Always when backup fails + affected locale.

Additional context

• Crashes only when backup failure notification path runs; backup failure itself may be a separate issue.
• formatPlural has no try/catch; invalid translation pattern is fatal.
• Audit all locale variants of settings__backup__failed_message for ICU plural syntax.
• Tracked under epic [Epic] Play production crashes — mainnet 2.2.0 (build 181) vitals triage #986.