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Note that the Ö/Ø Morse code is an O (—) followed by an E (·), usually written as OE. OE also happens to be how the letter is written if the proper symbol isn’t available. That also shows the relationship with the French Œ, but that’s a digression that has little to do with Morse code. Likewise, the Morse symbols for both the Ä/Æ and the Ü start with the non-accented letter and are AA and UT respectively.

Here also there is a nice pattern for how many of these symbols are formed. Take Esperanto as an example, where the symbols are all formed by appending a short letter to the original one: Ĉ is CE, Ŝ is SN (which also happens to be the prosign for ‘understood’), Ĝ is GN, and Ĵ is JE. The Polish  Ł and Ż follow the same convention and are LT and ZT respectively, and so does the Nordic Å which is AK.

There are also six-symbol combinations in Polish: Ź which is –⋅⋅-⋅ (ZN) and Ś which is ⋅⋅⋅-⋅⋅⋅ (SB). The German Wikipedia even lists a Morse code for the double S: ß, ⋅⋅⋅–⋅⋅ or SZ, but I believe two consecutive S’s work well or even better.

I recently asked on the Elecraft list if the K3 Morse decoder could support some of these letters, and I asked specifically about Ä/Æ, Ö/Ø, Å, and Ü. These are the four which are shown in the first figure in the upper right-hand corner of this post.

But which ones do you think are the most important ones to include in Morse software?