“Riyadh-us-Saleheen” is an authentic and reliable book by Imam Nawawi on Hadith. It is a compilation of hadith related to beliefs, manners, etiquettes, social relationships etc. It is better if you read it before any teacher (Alim) as lessons as it will save you from mistake and benefit you a lot. But if you have the understanding of Arabic language to an extent that you understand the basic moral and religious books then it shall be alright for you to study it provided you highlight the place where you are unable to understand or you have any doubt and later get it understood from any Alim.
If you want to know about reading the translation of Riyadh-us-Saleheen in any other language except of Arabic such as Urdu, Bengali, etc then first let us know who has translated it and seek the advice of local Ulama whether it is good to read the translation or not. As sometimes the translator mistakes and the reader considers it the meaning of hadith; that is why the authenticity of the translation matters.
Allah knows Best!
Darul Uloom Deoband