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
- Cbb: written as »Ceses«, spoken: [ʦeses]
- Cb: »Ces«, [ʦes]
- C: »C«, [ʦeː]
- C#: »Cis«, [ʦis]
- C##: »Cisis«, [ʦisis]
- D Note
- Dbb: »Deses«, [deses]
- Db: »Des«, [des]
- D: »D«, [deː]
- D#: »Dis«, [dis]
- D##: »Disis«, [disis]
- E Note
- Ebb: »Eses«, [eses]
- Eb: »Es«, [es]
- E: »E«, [eː]
- E#: »Eis«, [eːis] (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«, [eːisis]
- F Note
- Fbb: »Feses«, [feses]
- Fb: »Fes«, [fes]
- F: »F«, [ɛf]
- F#: »Fis«, [fis]
- F##: »Fisis«, [fisis]
- G Note
- Gbb: »Geses«, [ɡeses]
- Gb: »Ges«, [ɡes]
- G: »G«, [ɡeː]
- G#: »Gis«, [ɡis]
- G##: »Gisis«, [ɡisis]
- A Note
- Abb: »Asas«, [asas]
- Ab: »As«, [as]
- A: »A«, [aː]
- A#: »Ais«, [aːis]
- A##: »Aisis«, [aːisis]
- B Note
- Bbb: »Heses«, [heses]
- Bb: »B«, [beː]
- B: »H«, [haː]
- B#: »His«, [his]
- B##: »Hisis«, [hisis]
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.