Thank you very much Pete, this was a part of the solution.
Actually, what I found out on a German forum for RoboHelp, is
that one has to set the machine on the regional settings for the
country for which the localisation is being done. I installed the
support language pack previous to my problem and so I was able what
I was translating in the topics. The problem appeared when I tried
my first compilation. The topics were still in Japanese, as I
translated them, however the TOC and the index were the only ones
which were in a totally unknown writing style (not Japanese and not
English and not any other language I know).
Right now as I changed the localisation of my system, it
works.
So, I think this should be a first improvement for RoboHelp,
right? They brag that they support 35 languages, however the
support is not quite... complete, eh?
By the way, the error message keeps coming even after all
those changes, however I do not care too much about it, as I get
what I need.
Thank you again Pete for the solution and the fast
answer.