Hi again Florian.
I have a question about ReplayGain and Mp3tag. I have started using Frontah to add ReplayGain(Album) to my MP3 collection. I need to do this for about 250 Albums (Ouch!). I see that after I add ReplayGain the files have an APE tag that wasn't there before. So I presume the ReplayGain info for MP3 is stored in APE Tags. I don't seem to be able to view this ReplayGain data in Mp3tag, but I can see it in Frontah, so I know it's there. Is this a feature you might add in the future?
Also, do you have any plans to implement ReplayGain calculation from within Mp3tag?
Unless there is an easier way of doing it that I don't know about, I think I'm going to have to sit here for quite along time adding ReplayGain for each album individually using Frontah. It's going to take ages.
What would be amazing is if I could open my top level MP3 folder, which is my entire collection of MP3's, click a couple of buttons in Mp3tag and have it do all the work for me. That would be very nice!!! I'm not a programmer but if Mp3tag used replaygain.exe the way Frontah does I guess this might not be too difficult to implement?!?! Although, I could be wrong of course. 
Thanks again.
By the way, I just spotted that Mp3tag is listed on Tucows with 5 stars. Congratulations!