From the WBCS eligibility rules:

📌 Bengali Language Clause

• A candidate must be able to read, write and speak in Bengali.
• Exception: Candidates whose mother tongue is Nepali are exempted from this requirement.
• This test is done at the time of the personality test or interview.

👉 This means Bengali proficiency is mandatory for all except Nepali-speaking candidates.

More can be learned from the link below:

Course Links:

• Prelims + Main + Interview (Classroom Foundation Course)  weekend batches, Specially beneficial for students / officer goers / those want matured guidance. 
• Prelims + Main + Interview (Online Foundation Course)  weekend batches,  – Specially beneficial for students / officer goers / those want matured guidance. 
• New course for Maths & Reasoning, weekly once, 6 months .
• Mock Test for Prelims (35 tests), online / classroom available. 
• WBCS Prelims Subject Wise Chapter Wise Mock Test
• Mock Test for Main Exam, online / classroom available. 
• Correspondence course for WBCS . 
• Crash Course for WBCS Main exam . 
• Optional Subjects (weekly once, 6 months).