Urdu and Sindhi is Missing in System Support Langauges in Ubuntu 20.04
Solution 1:
Those two languages have not been selectable in Ubuntu since Ubuntu 14.04, and the reason is that they both have very few translated strings while we nowadays apply a 5% threshold.
You may want to help revive respective translators team, with the goal to achieve at least 5% translation coverage.
https://launchpad.net/~ubuntu-l10n-sd
https://launchpad.net/~ubuntu-l10n-ur