Hello,
thanks for all the information you gave me!!!

Before I posted here, I tried the library at my home town. But there was not a single book about Irish place names or the Irish language. I did not only look on the shelves, but also in the computer-based catalogue which allows wildcard searching which I used heavily - I think if there is such a book it is not in the catalogue. (The problem might be that I am in a country with very few people with Irish ancestors: Germany)
The topic is not that important to me that I would invest any large sum of money in it - I did not find anything on the topic in the bookstores, also not in their catalogues of German books.
That is why I tried to gather the information here - sorry if I offended anyone with that.

MudGuard