About the novels
How many volumes are there?
There are currently 18 volumes in Japan, plus some special volumes: vol 0, vol 0-II vol 2.8 and vol 5.5. For the English release there are 10 volumes, with volume 11 being expected to come out on the 21st of August.
Where can I buy read the novels?
The novels have been licensed by Yen Press. You can buy the hard copy at your local bookstore or buy their eBook online. For those who try to save their money, Book Depository is a great place to order. It has free shipping worldwide and often has discounts on their products.
Isn't there any fan-translation that I can read?
Yes, but this isn't the place to ask for links. It's fine to read the free fan-translations, but the translator expects you to support the author by buying a legal copy. Do note that randomly posting links to free translations can bring the translator in trouble too.
Will we get an English translation of the special volumes?
It's very likely that volume 0 and 0-II will get an official translation, since they're part of the main series, the other two however will probably only get fan-translations. Volumes 2.8 and 5.5 weren't available for sale in Japan as they came together with the DVD/ Blue-Ray of the anime. That is why it's very unlikely for them to have an official translation.
About the anime adaptation
How much of the novels has the anime covered?
The anime only covered volumes 1 and 2 of the novels. This is probably done, because the first two volumes are introduction arcs, to make the reader familiar with the characters and setting.
Is there a season 2?
No.
Will there be a season 2?
We're not certain. As of now we have found no news or rumours about a second season. The original purpose of the anime, was to promote the light novel and boost its sales, which was obviously a success and now that the novels have reached the western audience, maybe if we show our support by buying the novels they will consider a second season.
About the manga adaptation
There is a manga?
Yes, an official manga adaptation by Akio Hiragi and a spin-off series called, Hataraku Maou-sama! High School! by Mishima Kurone. The High School spin off has also gotten a Novel adaption which was written by Wagahara, however it does not follow the exact same plot as the manga.
Do these manga adaptations also have an English translation?
Yes, Yen Press is also releasing the English translation of these two manga.
How many volumes are there?
The manga adaptation currently has 13 volumes in Japan. These 13 volumes cover the first five volumes and a special volume. Yen Press has currently released ten volumes, and volume 11 is expected to come out on the 22nd of May.
As for the Spin-off, Hatamaou! High School, it has five volumes in Japan and is completed. Yen Press has translated all five volumes of the Spin-off.