Jawaharlal Nehru University

The eligibility criteria of B.A. (Hons.) in Japanese of JNU is given below.
Eligibility Criteria : A candidate must have passed the Senior School Certificate (10+2) or equivalent examination with a minimum of 45% marks. The candidates who are due to appear in Senior School Certificate (10+2) or equivalent examination are eligible to apply.
Admission criteria : Entrance test. The entrance test for this programme is a common test for all languages. Questions pertaining to general knowledge, artificial language, language aptitude and general English would be covered in the syllabus. The test will be conducted in the English language as a Computer Based Test (CBT).
So from above prior knowledge of the basic Japanese language is not essential for the asked program.

The eligibility criteria of M.A. in Economics (Specialization in World Economy) of JNU is given below.
Eligibility criteria :
(i) Bachelors degree (with 50% marks in aggregate) in the following subjects: Economics (Hons.) with
Mathematics as a subsidiary subject; or Mathematics (Hons.) with Economics as a subsidiary subject; or
Statistics (Hons.) with Economics and Mathematics as subsidiary subjects.
(ii) Any other Bachelors degree (with 60% marks in aggregate) with courses in Microeconomics,
Macroeconomics, Mathematical Economics and Statistics.
So from above Bachelor degree in Economics (Hons.) with Mathematics as a subsidiary subject is needed for M.A. in Economics (Specialization in World Economy), hence you are not eligible for the asked course.