Why developers plateau
A developer who types 90 WPM in prose often manages barely half that in code. The bottleneck is almost never the letters — it is the symbol reaches, the shifted characters and the constant switching between alphabetic and punctuation zones of the keyboard.
Choosing a practice language
Practise the language you actually write. The symbol distribution differs sharply: JavaScript is dense with braces and arrows, Python with colons and underscores, SQL with uppercase keywords, and HTML with angle brackets and quote pairs. Training on the wrong distribution builds the wrong reflexes.