What are the most common keyboard layouts and why is each layout designed as such? - Honor 9X Guides, News, & Discussion

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The QWERTY layout is the most popular option, but there are also AZERTY and QWERTZ keyboards, as well as many others…
This question is quite difficult to answer, much like how hard it would be to list the most common global languages and explain the rationale for each language's characteristics. This is because it can be tricky to define what "common" even refers to, as keyboard designs are heavily affected by the various letters and diacritical marks used in languages.
For the Roman/Latin alphabet, QWERTY, AZERTY and QWERTZ are the three most widely-accepted layouts. Even this distinction fails to grasp the complexity of the issue, as each of them has their own variants. For example, this is a standard U.S. QWERTY keyboard:
And this is a standard QWERTY keyboard used in Spain, accommodated for the diacritical mark "ñ" used in Spanish:
As these examples suggest, the QWERTY standard has been adapted for a wide range of countries and regions, including customized designs for Brazil, Portugal and the U.K. The variants tend to differ dramatically in the numeric keys, as well as with regard to special characters and symbols.
Another popular keyboard layout, the QWERTZ, is used rather extensively in Germany, and other countries with close historic and cultural ties to Germany. A German QWERTZ keyboard looks like this:
Here is QWERTZ tailored for Switzerland, with a layout that provides the user with the flexibility to type in either German or French:
The major difference between QWERTZ and QWERTY is that the Y and Z keys have changed position – mainly because T and Z often appear together in German spellings, and would be too difficult to type with one hand. In QWERTZ, T and Z can be easily typed with separate hands.
Now we've come to the AZERTY keyboard (used primarily in France):
AZERTY is also a reworking of QWERTY, having switched the positions of the A and Q keys, W and Z keys, and relocated the M key. The reason for these changes is... a mystery to me! Even experts have not reached a consensus on this, and no single answer definitely explains why AZERTY was specially made for French people. It's theoretically less efficient than QWERTY for several reasons – for instance, A appears a lot more frequently than Q, but is placed in a difficult-to-access position. A much-subscribed theory posits that the first typewriter manufacturers opted for AZERTY, for whatever reason, and France has been stuck with it ever since…
The map below shows the popularity of QWERTY, QWERTZ and AZERTY in Europe:
Green: QWERTY
Blue: AZERTY
Orange: QWERTZ
Yellow: a country's own standard
QWERTY is without question the closest thing to a universal standard keyboard layout in most countries. You've probably noticed that Italy, Portugal and Turkey are marked with two colors. These three countries originally had their own standards, as home computers needed to adopt local typewriter keyboard layouts to attract local market share – yet eventually QWERTY took hold as IBM increased its global reach.
This is Italy's typewriter-based QZERTY in the old days, to be later replaced by QWERTY:
Turkey had its own standard as well, a keyboard design called "Turkish-F":
The invention of "Turkish-F keyboard" can be traced to an American educational psychologist named August Dvorak, who denounced QWERTY as an unreasonable design and created the so-called "Dvorak keyboard" as an alternative. His proposal didn't catch on in his home country, but made some waves in Turkey, where ongoing studies in bone and muscle anatomy had been leveraged in designing the optimal keyboard layout for Turkish, at a time when Turkey was looking to abandon the Arabic alphabet in favor of Roman letters. The Turkish-F really went viral… for a time, before being phased out for QWERTY, due to the personal computer revolution.
Now let's look back at what Dvorak objected to about QWERTY… It all started in the 1860s, when a young man named Christopher L. Sholes invented the first-ever typewriter, drawing inspiration from the existing concept of movable type:
However, the structure of that typewriter often caused it to jam (as shown below), which would occur when two adjacent keys were pressed simultaneously:
Sholes then set about reorganizing the letters and uncoupling common letter combinations, such as WH, TH and AD, to solve the jamming issue – and hence, the QWERTY keyboard was born.
Sholes' company went bust after selling about 5,000 typewriters, and he sold his patent to a businessman, who persuaded the famed gun manufacturer E. Remington and Sons to purchase Sholes' invention for a lavish sum. This paved the way for the groundbreaking Remington Standard No. 2, a significant improvement upon Sholes' product, as it completely eliminated the presence of jamming. However, given the presence of 5,000 Sholes typewriters in circulation, Remington didn't want to disrupt consumers' habits, and opted to retain the QWERTY layout.
Remington Standard No. 2 was the gold standard for typewriters, selling 100,000 units annually by the year 1900. That's when Sholes approached Remington with the offer of a more scientifically-based keyboard layout that could substantially increase typing efficiency. Unfortunately, Remington rejected the new idea, as hundreds of thousands, if not millions, of people had already grown accustomed to using QWERTY.
That brings us to the 1930s… when August Dvorak carefully studied the letter frequency in the English language, and devised a layout in which the most commonly-used letters were placed in the middle column of the typewriter, so that pressing these letters would require minimal finger movement. The column above houses the less common letters, and the column below is reserved for the least frequently-used letters. The vowels (A, E, I, O, U) are grouped on the left, and consonants on the right, so that the user types with alternating presses from fingers on their left and right hands:
The image below shows the typing frequency of the keys on a QWERTY keyboard:
Here's what it looks like under Dvorak's design:
The French also adapted Dvorak's design for a BÉPO keyboard:
The Germans designed the NEO layout, also based on the Dvorak keyboard:
Dvorak even came up with a one-handed layout, designed specifically for war veteran friends of his, who had lost their arms in battle:
Therefore, Dvorak's design is an extremely handy frame of reference for keyboard layout designers to enhance the efficacy of their own models.