It depends. If the translator died before 1954 (70-year rule in Sri Lanka), their work is public domain and free. If it’s a modern translation (e.g., published in 2010), downloading a full copy without paying is copyright infringement.
Most readers in Sri Lanka follow translations by , who has translated over 29 books in the series. Bihisunu Nimnaya : Translation of The Valley of Fear . Siwu Rahas Salakuna : Translation of The Sign of Four . Sherlock Holmes Books Sinhala Pdf Free Download