chore: add sinhala to localizer

[tlebon]

Description

add missing language to localizer

Checklist

• PR has been self reviewed by the author;
• Hard-to-understand areas of the code have been commented;
• If it is a core feature, unit tests have been added;

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.04%. Comparing base (876501f) to head (2a9bd77).
Report is 180 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #17372      +/-   ##
==========================================
- Coverage   46.13%   46.04%   -0.10%     
==========================================
  Files         747      753       +6     
  Lines       24555    24738     +183     
  Branches     5611     5670      +59     
==========================================
+ Hits        11329    11391      +62     
- Misses      11793    11917     +124     
+ Partials     1433     1430       -3