Hi, and thank you for your interest!
Stopwatch is being translated using Weblate, a web tool designed to ease translating for both developers and translators.
Translation project for Stopwatch into Sinhala currently contains 47 strings for translation and is 2.1% complete.
If you would like to contribute to translation of Stopwatch, you need to register on this server.
Once you have activated your account just proceed to the translation section.