Add Sinhalese as available language

What does this MR do and why?

We have reached 11% of translated and approved strings for Sinhalese.

This MR adds Sinhalese as available language to our UI as per our guidelines.

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.