J was introduced because I had a similar problem, except I could be either a consonant or a vowel, rather than any of two consonants. The same applied to the introduction of U for V. Well, almost the same. In the case of I, they added J to be the consonant, while in the case of V, they added U to be the vowel.

Finally, people changed the pronunciation of V over time to be something new, and W was introduced to be the original sound in English. W does not exist in Latin since V fulfills its role, unless you are using a modern pronunciation that changes how V is pronounced and then you still do not need W. There were other sound changes (see Italian), but this is sufficient to explain all of the letters. Well, there is also Z, which they removed from early Latin and later reintroduced to represent a Greek sound.

The original Latin alphabet had 21 letters:

ABCDE FZHIK LMNOP QRSTV X

The letter V (Greek u-psilon) was used to write the sound U, both as vowel and as consonant (i.e. like English W).

The letter F (Greek di-gamma) was used in Greek for consonant U (English W), but in Latin it was used to write the sound F, also a labial consonant, which did not exist in Greek.

In Latin, in the beginning 3 different letters were used to write the sound K, C before E or I, K before A and Q before O or U. So K belonged to the Latin alphabet since its very beginning.

Later, the rules for writing K have been simplified, so it was always written as C, except before a V (i.e. U sound) that was consonant, not vowel, i.e. like English W. Writing K has been retained only in a few traditional expressions, e.g. in "KALENDAE", which was used when writing dates.

Initially, the letter C (Greek gamma) was used both for the sound K and for the sound G. Later, the letter G has been created, by modifying the letter C. Since then, G was used for the sound G, except in a few traditional expressions, e.g. the name "Gaius" has continued to be written as "Caius", together with a few other traditional names.

The new letter G has substituted in the Latin alphabet the letter Z (Greek zeta), which was not used in Latin. Therefore the 21-letter Latin alphabet has become:

ABCDE FGHIK LMNOP QRSTV X

Several centuries later, during the Roman Empire, 2 additional Greek letters have been added at the end of the alphabet, so the 23-letter Latin alphabet was:

ABCDE FGHIK LMNOP QRSTV XYZ

The letter Z was reintroduced, but not in its original place, because it was contained in some borrowed Greek words. The same with Y. While both V and Y come from Greek u-psilon, by the time when Y has been added to the Latin alphabet it was pronounced as a vowel different from both Latin V and I, i.e. as a front rounded closed vowel, like the Scandinavian Y, German Ü (U with Umlaut) or French U.

The 23-letter Latin alphabet has become a 26-letter alphabet more than a millennium later, when the letters J, U and W have been added (J and U were required because in the Romance languages the old I consonant and U consonant had become fricative sounds, completely distinct from the I and U vowels, while W has been initially added for English, which is one of the few Indo-European languages that has retained the original pronunciation of consonant U).

"W" was added originally by northern Germanic languages, including English, replacing the practice of writing the same sound with a doubled "u" or "v". Which explains both its appearance and its name in English and many other languages.

Like all things I don’t understand, I suspect fashion was heavily involved when the decision was made.

Also, ß is ss and since words don't start with Ss there is no need for an uppercase ß. When whole words are capitalized ß turns into SS.

Of course there is a little edge case where capitalization isn't reversible. For example, is the capitalized version of the name MASSMANN to be converted to Maßmann or Massmann? That is in my opinion the only reason the uppercase ß was added to Unicode. To resolve this ambiguity. It has no place in proper German typography.

The script that came to be known as Cyrilic was developed by Cyril and Methodius' followers, after they were exiled from Great Moravia (by the bishop that replaced Methodius), so it's safe to assume that those in that group were not Bulgarians either.

Some names today still use the double a, like the Norwegian football player Martin Ødegaard. In that case it is pronounced the same as the "å" sound. (not too far from how an American might pronounce the "o" sound in "for")

While some script are deliberately designed, most are a result of gradual evolution.

https://news.ycombinator.com/item?id=42837273#42882295