The German sequence of the basic notes (white keys on piano) is: C, D, E, F, G, A, H.
The system is simple. There is no »flat« or »sharp«, just the suffixes »-es« and »-is«. And you have to keep in mind, that the German name of the English B is H. There are five exceptions, they are written in boldface.
I will not talk about enharmonic, I guess you know about it.
- C Note
- C♭♭: written as »Ceses«, spoken: [t͡sɛsɛs]
- C♭: »Ces«, [t͡sɛs]
- C: »C«, [t͡seː]
- C♯: »Cis«, [t͡sɪs]
- C♯♯: »Cisis«, [t͡sɪsɪs]
- D Note
- D♭♭: »Deses«, [dɛsɛs]
- D♭: »Des«, [dɛs]
- D: »D«, [deː]
- D♯: »Dis«, [dɪs]
- D♯♯: »Disis«, [dɪsɪs]
- E Note
- E♭♭: »Eses«, [ɛsɛs]
- E♭: »Es«, [ɛs]
- E: »E«, [eː]
- E♯: »Eis«, [eːɪs] (do not mix up with [aɪ̯s]! Later is the pronunciation of the German word for ice or ice creme, not for the music note)
- E♯♯: »Eisis«, [eːɪsɪs]
- F Note
- F♭♭: »Feses«, [fɛsɛs]
- F♭: »Fes«, [fɛs]
- F: »F«, [ɛf]
- F♯: »Fis«, [fɪs]
- F♯♯: »Fisis«, [fɪsɪs]
- G Note
- G♭♭: »Geses«, [ɡɛsɛs]
- G♭: »Ges«, [ɡɛs]
- G: »G«, [ɡeː]
- G♯: »Gis«, [ɡɪs]
- G♯♯: »Gisis«, [ɡɪsɪs]
- A Note
- A♭♭: »Asas«, [asas]
- A♭: »As«, [as]
- A: »A«, [aː]
- A♯: »Ais«, [aːɪs]
- A♯♯: »Aisis«, [aːɪsɪs]
- B Note
- B♭♭: »Heses«, [hɛsɛs]
- B♭: »B«, [beː]
- B: »H«, [haː]
- B♯: »His«, [hɪs]
- B♯♯: »Hisis«, [hɪsɪs]
Addendum
The sign ♯ (that looks very similar to the sign #, but is different to it), which is written in a staff before a note's head to mark it as being a halftone higher, is called »Kreuz« ([kʀɔɪ̯ʦ]). This sign can also be part of a staffs key signature.
The sign 𝄪 before a note's head marks it as two halftones higher and is named »Doppelkreuz« ([ˈdɔpl̩ˌkʀɔɪ̯ʦ]) in German. This sign can not be part of a staffs key signature.
To mark a note as one halftone lower, you use the sign ♭ before a notes head or in the key signature. Since it looks like the letter b (from which it is different!) it is named »B« ([beː]) in German.
To make a note two halftones lower you use the sign 𝄫 (before a notes head only, never as part of a key signature). It's German name is »Doppel-B« ([ˈdɔpl̩ˌbeː].
To cancel all four of these signs there is the sign ♮ (which also looks similar to #, so be careful with that!). Its German name is »Auflösungszeichen« ([ˈaʊ̯fˌløːzʊŋsˈʦaɪ̯çn̩]]) (verbatim: annulment-sign). But be careful: This sign has barely nothing to do with »resolution« (of a dissonant accord into a consonant accord), with is »Auflösung« in German too.