Are there any good reason to learn languages such as Ada and COBOL? Are there any future in programming in those languages? I'm interested in those languages and i'm currently learning them just for fun.
Its always worthwhile learning new languages. Even if they're never useful to you professionally chances are they'll teach you something about programming you didn't know before or at very least broaden your outlook.
As for prospects from a quick bit of reading around it seems ada is still somewhat in favour for critical systems in the aviation industry and Cobol still has its place in business. I know an engineer in his mid 20's who writes all his code in fortran77 as that's what industry wants!
While the number of employers looking for these languages might be low, because there are a limited number of people who know them the salary for developers who specialise in them can be quite high. When mission critical apps developed in them could cost millions to replace having to pay more than usual for a coder to maintain the existing system is easily accepted.