There seems to be a sale of sorts on Harry Potter books in the UK. It doesn't offer much off, but the books rarely go on sale at all. YMMV!
The collection of the seven main books is on sale at £31.99 (down from £37-ish), in at least three languages: English, Spanish and French. The individual titles also seem to be down by £1.00, from £5.99 to £4.99, at least for the few I spot-checked. The £31.99 is a bit better price than 7 x £4.99 = £34.93 if you need them all. It is also actually quite a good price compared to the standard US $57.99 at Kindle US and Pottermore, where there doesn't seem to be a sale. (My exchange rate site says £31.99 is about US $39.97 right now...)
I've found that reading HP in French has really helped my French, so I've been eyeing HP in Spanish, and I'll probably bite on the seven-book Spanish collection.
I haven't checked any of the other titles in the HP universe, like
Tales of Beedle the Bard or
Fantastic Beasts.
Anyway here are links for the three collections, and if you want individual titles you will have to search for them yourself.
Harry Potter: The Complete Collection (1-7)
Kindle UK:
https://www.amazon.co.uk/gp/product/B01B3DKROQ/
Kobo UK:
https://www.kobo.com/gb/en/ebook/har...llection-1-7-1
Harry Potter: La Collection Complète (1-7)
Kindle UK:
https://www.amazon.co.uk/Harry-Potte...dp/B01B6RN7FK/
Kobo UK:
https://www.kobo.com/gb/en/ebook/har...n-complete-1-7
Harry Potter: La Colección Completa (1-7)
Kindle UK:
https://www.amazon.co.uk/Harry-Potte...dp/B01B6RN6J2/
Kindle US:
https://www.kobo.com/gb/en/ebook/har...n-complete-1-7