Romy,
I will give it a shot but am fully aware that this is rather a guess and I would need other views of this including better view of the tail and a clear uncluttered shot of the head. This appears to be in either Acrocephalus or Locustella. Certain features are better applied to either of these two genera. My guess is that it may be Locustella and my preference would be to Locustella fasciolata. Having stuck my neck out, this definitely needs a better analysis by someone more familiar with these types of confusing Sylvids.
